"Anyway what she has or hasn't done in the past doesn't really come into it. "
In legal terms, you must know it absolutely does make a difference. The entire basis of previous character is based upon it. And in terms of the school's attitude, a one-off is hugely different from a course of conduct, too. The former may make her someone who has had a terrible day/week and acted completely uncharacteristically, and the latter makes her a regular bully of smaller children.
"I think part of the problem is that we are getting a partial account, second or third hand of a scrum type situation. The OP's daughter has given her side of events, but we can't hear the other side or how she perceived the situation. "
No, part of the problem is posters are ignoring the words actually given in favour of their own assumptions. It bemuses me. Why bother commenting on a post if you construct your own alternative scenario instead of facts actually supplied?
"Of course what she did was wrong, but I think that the call the Police/Private prosecution route is in the case of the former a sledgehammer to crack a nut and in the latter absurd/impossible."
I agree, and I stated as much in some detail in previous posts.
"IF this girl is identified and unless she's got a track record of this sort of thing, a stiff bollocking and a few weeks on report seem about right, along with a firm reminder to the year 7s not to mess around in the corridor. "
But I thought "what she has or hasn't done in the past doesn't really come into it"? So why does her track record suddenly matter? And if she has deliberately punched a smaller child in the face without provocation, she needs to be suspended. If it was a one-off response and she has some underlying extenuating circumstances, then I'd agree with a stiff bollocking and being on report. If this is a course of conduct it's risible to believe that a telling off and a bit of detention will mean a thing to her, why would it? Though for the record, I'd also want someone to look at what is going on with her. She may need some support as well as some discipline. This behaviour is not, in my view, normal. More common than we'd like, but not normal either. She may have issues of her own that need addressing alongside.
"I can understand the OP's distress, but really can't understand the baying for blood on this forum,what will criminalising a 14 year old child achieve, apart from making her virtually unemployable when she leaves school?"
I agree it would be complete overkill (and actually I think crininalising her would be likelier to entrench the behaviour than change it - labelling theory, and all that) but let's be serious, she'd be unlikely to be charged with anything unless she has existing form, and cautions are spent at once if simple/inside 3 months if conditional, so employability wouldn't be affected if they took that route. And as you know, juvenile convictions are generally spent pretty quickly anyway, so would usually only be known to an adult employer if an enhanced CRB were required. (And in any event, I know someone who cheerfully lied to their employer over their student-era cannabis conviction, before it was spent. Without a CRB check requirement, an employer has to take your word for it.)
My advice remains the Head, the Governors and then a formal complaint to OFSTED, if the school aren't taking such an incident seriously. That's what those systems of complaint are there for. But the OP is very sensibly giving the school time to resolve it before looking for further steps.
OP, good luck with all this and I hope the GP reassures you. Also hope the schoool handle it properly, for everyone's sakes - including the girl who did it. She needs intervention, I think. And your daughter needs to feel safe and protected in what is basically her workplace.