Yes, if there is no prospect that she can sit for the performance, then she should not be in a seated audience. If it's a ballet school show, then there may well be a part of the hall at the back where she can run around without impeding the view of the proud relatives of the performers.
If it's a professional performance, it might be worth trying to resell her ticket (or take a friend of the 8yo) and try again en famille another year when she is ready.
Standing on chairs is too much even for a children's performance. And definitely a no-no for a regular matinee.
If you seriously think that she will stand on her chair or try to dance through the performance (I presume that means she is hardly going to be particularly quiet either) then please, for the sake of the rest of the audience, don't take her. Peter Pan is a popular family title but it is still a professional ballet and all the people around you who have paid £20 or £30 for their seats will be less than enchanted by her antics.
All my plans were for nothing, she sat silently entranced the whole performance, and danced around the Victoria center doing lovely ballet moves through the lghts tour afterwards.
Today she told everyone about the crocodile, and she didn't like the pirates.
