Meltdown or tantrum?

I think the main difference between a tantrum and a meltdown is that a tantrum is attention seeking, an attempt to get your own way, whereas a meltdown is the result of mental or physical overload, and requires time out and quiet. But she needs to learn how to control her tantrums, especially if she may harm someone or herself.

I don't think it's possible to "discipline" a meltdown, only to try to alleviate the cause.

As nexus9 has already said, she may need to be removed from the situation, or be encouraged to vent her anger at something else. For example, "stress balls", tearing up newspapers or thumping cushions works for my son.

Interrupting his special interest (computing) always provokes anger, but it can be much reduced by giving him at least 15 minutes prior warning of the change, with a reminder every 5 minutes. (I realise you may well already be doing something like this yourself, but thought it worth mentioning in case.)

I don’t think it’s attention seeking, she never does it at school, it’s only happened once out of the house. It’s never because she wants something like toys or sweets (infact she’s very good at knowing no means no), it’s nearly always because she is either worried about something or because she can’t control the situation. I just wonder if things like wanting to choose what to watch on tv is her being a madam or her having already planned it out in her head.

we do count downs and reminders when possible which do help, I think I need to get a firmer grip on this whole routine thing. I never really thought she was that routine led but maybe she’s just not telling me!

Hi school holidays are also a serious problem in my house as the amount of free time is just to much to handle. 

I also suffer the same issue with the girls in that the younger one (6) quite rightly wants her turn at things and to use her ideas for games but the older one (7) gets really angry that it's not right so lashes out so naturally the little one copies and all hell breaks loose! 

I try and explain it that they are both different and that we will take turns at set times ( sometimes works) but the younger one is getting very resentful as she sees it as the other getting more attention (especially since the older one is up most of the night and will only sleep with me) and I hate fact that in a way she is right. I try to make time for them separately this seems to help with the oldest ones sense of routine 

But we are now struggling after school as she spends so much time trying to fit in that she is literally a time bomb when she comes home 

You are definitely not alone in this 

Hi school holidays are also a serious problem in my house as the amount of free time is just to much to handle. 

I also suffer the same issue with the girls in that the younger one (6) quite rightly wants her turn at things and to use her ideas for games but the older one (7) gets really angry that it's not right so lashes out so naturally the little one copies and all hell breaks loose! 

I try and explain it that they are both different and that we will take turns at set times ( sometimes works) but the younger one is getting very resentful as she sees it as the other getting more attention (especially since the older one is up most of the night and will only sleep with me) and I hate fact that in a way she is right. I try to make time for them separately this seems to help with the oldest ones sense of routine 

But we are now struggling after school as she spends so much time trying to fit in that she is literally a time bomb when she comes home 

You are definitely not alone in this