ASD daughter being hit only daily basis in special unit

Hi, I am new to the forum but would like to know people opinions and advise, & what you may do in the same situation.

My daughter has started a special unit within a mainstream school, she started mid September, the hitting and pulling of hair started as a very occasional occurrance and I was reassured by my daughters teacher that this is a settling period all children go through and use as an excuse to get out of school, I excepting this answer for then, but the hair pulling by 1 child in particular has become very very frequent, up to the extent of 6 separate occasions in 1 day!! Now another child has started to hit kick and pull my daughters hair, whether this other child is taken the lead of the hair pulling child I don't know, but I no longer except that this is settling in excuses. 

I have approach my daughters teacher on 2 separate occasions with my concern and although I totally appreciate that all the children in the unit have their particular difficulties, I do not believe that my daughter should contend with this every day. I have been told that the hair puller has 1-1 and they are doing all they can to sto this behaviour and they know that it's unacceptable but that MY DAUGHTER has to learn to except other children's difficulties!!. 

I have since been to see the school head mistress who said she hears what I am saying and takes it on board and will talk to the teacher with regards to every child in the unit getting the same learning opportunity!! This really wasn't what I was expecting to hear. As far as I  concerned if the child has 1-1 and unfortunately the occasion has arised that they haven't got there in time to stop my daughters hair from being pulled then they should be aware of how volatile that child's behaviour is that day and be more aware of her actions and patterns of behaviour leading upto it.

I was also like to add that my daughter is ASD Asperger's syndrome, has extreme difficulties in with sensory processing and is taking anti depressants for her severe anxiety. She went to a mainstream nursery and infant school and we struggled immensely to get her their everyday, it became obviously apparent that she had a difficulties of some sort. She finally was diagnosed in 2014 and on moving on to junior school her anxiety hit breaking point and she lasted only 12 hrs in school before the school declared they couldn't cope with her disruptive behaviour and we withdrew her from school. We had a go at home school for a full 15 months while fighting for a statement which she was awarded in july this year.

We find it extremely difficult to get her to school anyway without the fear of being hurt once she arrives there to contend with...I hate that my daughter is feeling unsafe at school. 

I totally understand that excluding the children who are hurting my daughter would not help the child in the slightest and it is also what I don't expect, but I also do not believe aenough is being done to stop this.

.any advise would be greatly appreciate.

Would you believe I was also told that the reason she has her hair pulled is because she doesn't have it tied back!!