Whilst the school definitely have a responsibility to tackle bullying/the bullies, the person with the ultimate responsibility for what they have done is the bully. There is an issue with always shifting responsibility for their actions (or inaction- such as not doing coursework) away from young people onto someone (anyone) else. We aren’t doing them any favours by doing that, just creating problems for them and for those who have to have any dealings with them.
In reality, this might have shown this young person that her poor behaviour was not acceptable, that what she did not go unnoticed and that her wrong-doing to others was openly acknowledged. It might have shown her that actions have consequences that others don’t have to put up with poor behaviour (why should teachers give up their spare time planning and/or supervising something like prom for those children who behave badly).
Of course, she won’t have learnt anything at all if the important adults around her (I.e. parents/guardians) make excuses for her behaviour, blame the school and anyone/everyone else other than her and suggest that she had a right to attend this event, regardless of her behaviour because she is entitled to get what she wants in every circumstance.
I’d also point out that it means that her victim(s) get to attend the prom without the presence of the person who has been bullying them, which is surely the fairest outcome for these pupils?
All of which is totally different to schools applying attendance criteria to children whose attendance is low due to a medical condition or disability- allowances can and should be made for genuine reasons for not reaching the criteria for attendance.