Criminal offence

If this were my daughter, I'd be quizzing her as deeply as I know how to establish her state of mind.

Did she carry the knife to school to deter aggression? Did she have an actual plan? OR was it more of a half arsed " I gotta do something move". 

You really DO need to understand as her friend rather than as her parent why she did that thing. Use your partner to obtain a second opinion, encourage honesty, (even if it is not what you want to hear, stifle any negative reaction you have) as knowing the truth of the matter is most important.

You also need to work through all the possible scenarios for her / with her and get her to try and find the winning way of playing the "knife to school game" as an intellectual excercise.

Point out to her that now she has been NOTICED more than ever, was it really such a smart move? 

She's clearly trying to solve a very difficult problem using 13 year old brains, and what she could really use is help actively working the problem. 

I did not have that advantage when I was her age and was being ruthlessly bullied at school, indeed my home life was worse, so in fact I went the "psychotic violence as a deterrent" route between 8 and 11 until someone finally broke my nose, and I realised it was no deterrent, and worse I was in strife with teachers and seeing psychologists etc. none of which did I want to be involved in, so I switched from violence to psychology and avoidance of conflict strategies, which whilst they didn't make me feel much better about being generally persona non grata did win me a lot more peace and quiet, and time to do things "better" than fighting or trying to get along with people who had no time for me. 

Although being a bloke I did get occasionally "forced" into a fight, which I generally lost, and by the time I was sixteen I identified strongly as a "coward" unless I really had to physically defend myself, in which case I'd pick whatever tool, strategy or tactics I needed to make sure I was going to win and advance upon my opponent fully intent and focussed  on doing them an adequate level of harm. Those I always won.

By the time I reached my early twenties my coping skills and basic psychology was sufficient to avoid physical altercations altogether and apart for a couple of incidents involving loons & a mugging attempt all of which were dealt with by "managing the situation better than my would-be opponent".

She might as well accept that this is her burden, and finding ways to cope that do not involve harming or threatening to harm others is indeed the pinnacle of skill and she can use her autistic detachment plus learning skills to learn how to deal with others using psychology rather than cold steel. 

The support I got when I was being bullied, was "Find the biggest one, and smash him to the ground then look at the others and ask, Who's next?"

Whereas the correct advice would have been more along the lines of: "Go straight to the school office next time it happens and request an interview with the deputy head. Explain as calmly as you can what is being done to you that you do not like or makes you feel sad and unwanted, and make a point of giving them my mobile phone number and ask them to call me as soon after the interview as is convenient..." IF anyone calls you a "snitch" etc, calmly point out that if they don't want the trouble, ten just leave me alone, because if asking for help is what it takes to get them off your back, that is what you will do. Most importantly of fall make sure she reports any actual threats made against her to the same person immediately. Bullies fear "authority" more than anything else. 

That's my take on it FWIW, and it took me a LOT of effort to find a path that worked for me and those inevitable jerks you meet who, no matter how you try, will NOT like the cut of your jib.

But whatever you do, she needs to see the circular nature of violence, and she needs to know to NEVER pick up a deadly weapon unless she is fully committed to using it to kill someone. Killing someone because they "make you unhappy" is of course madness, so she needs to rule that out and find other solutions that will actually work. I'm living proof that those alternative solutions work, but she needs help working the alternatives out if her suffering is to be cut shorter.   

I've made assumptions based on your testimony, and I am optimistic that your daughter just made a dumb move, but she needs to know that people will want to interview her a lot for a while, and that she should just co-operate and tell the truth at all times in such interviews that may happen in order to make them leave her alone.

I'd definitely want my most legally competent person I could get my hands on to get their hands up the police sharpish and ask WHY they have charged your 13yr old  daughter... 

I hope my admittedly over informed and perhaps "alternative" take on the matter helps in some small way.

I tried very hard to use the right words to convey the meaning and nuances as best as I can.  

If this were my daughter, I'd be quizzing her as deeply as I know how to establish her state of mind.

Did she carry the knife to school to deter aggression? Did she have an actual plan? OR was it more of a half arsed " I gotta do something move". 

You really DO need to understand as her friend rather than as her parent why she did that thing. Use your partner to obtain a second opinion, encourage honesty, (even if it is not what you want to hear, stifle any negative reaction you have) as knowing the truth of the matter is most important.

You also need to work through all the possible scenarios for her / with her and get her to try and find the winning way of playing the "knife to school game" as an intellectual excercise.

Point out to her that now she has been NOTICED more than ever, was it really such a smart move? 

She's clearly trying to solve a very difficult problem using 13 year old brains, and what she could really use is help actively working the problem. 

I did not have that advantage when I was her age and was being ruthlessly bullied at school, indeed my home life was worse, so in fact I went the "psychotic violence as a deterrent" route between 8 and 11 until someone finally broke my nose, and I realised it was no deterrent, and worse I was in strife with teachers and seeing psychologists etc. none of which did I want to be involved in, so I switched from violence to psychology and avoidance of conflict strategies, which whilst they didn't make me feel much better about being generally persona non grata did win me a lot more peace and quiet, and time to do things "better" than fighting or trying to get along with people who had no time for me. 

Although being a bloke I did get occasionally "forced" into a fight, which I generally lost, and by the time I was sixteen I identified strongly as a "coward" unless I really had to physically defend myself, in which case I'd pick whatever tool, strategy or tactics I needed to make sure I was going to win and advance upon my opponent fully intent and focussed  on doing them an adequate level of harm. Those I always won.

By the time I reached my early twenties my coping skills and basic psychology was sufficient to avoid physical altercations altogether and apart for a couple of incidents involving loons & a mugging attempt all of which were dealt with by "managing the situation better than my would-be opponent".

She might as well accept that this is her burden, and finding ways to cope that do not involve harming or threatening to harm others is indeed the pinnacle of skill and she can use her autistic detachment plus learning skills to learn how to deal with others using psychology rather than cold steel. 

The support I got when I was being bullied, was "Find the biggest one, and smash him to the ground then look at the others and ask, Who's next?"

Whereas the correct advice would have been more along the lines of: "Go straight to the school office next time it happens and request an interview with the deputy head. Explain as calmly as you can what is being done to you that you do not like or makes you feel sad and unwanted, and make a point of giving them my mobile phone number and ask them to call me as soon after the interview as is convenient..." IF anyone calls you a "snitch" etc, calmly point out that if they don't want the trouble, ten just leave me alone, because if asking for help is what it takes to get them off your back, that is what you will do. Most importantly of fall make sure she reports any actual threats made against her to the same person immediately. Bullies fear "authority" more than anything else. 

That's my take on it FWIW, and it took me a LOT of effort to find a path that worked for me and those inevitable jerks you meet who, no matter how you try, will NOT like the cut of your jib.

But whatever you do, she needs to see the circular nature of violence, and she needs to know to NEVER pick up a deadly weapon unless she is fully committed to using it to kill someone. Killing someone because they "make you unhappy" is of course madness, so she needs to rule that out and find other solutions that will actually work. I'm living proof that those alternative solutions work, but she needs help working the alternatives out if her suffering is to be cut shorter.   

I've made assumptions based on your testimony, and I am optimistic that your daughter just made a dumb move, but she needs to know that people will want to interview her a lot for a while, and that she should just co-operate and tell the truth at all times in such interviews that may happen in order to make them leave her alone.

I'd definitely want my most legally competent person I could get my hands on to get their hands up the police sharpish and ask WHY they have charged your 13yr old  daughter... 

I hope my admittedly over informed and perhaps "alternative" take on the matter helps in some small way.

I tried very hard to use the right words to convey the meaning and nuances as best as I can.