like cheerforeverandever said, your coach might not feel comfortable supervising or teaching you guys stunting. I coach middle school cheer and they stunt. The most difficult stunt we do is a full, straight cradle. We will not do any more difficult stunts because I don't feel like they are ready for that. We still have a lot of kinks to work out with other stuff.
Your coach may just want you guys to focus on the spirit aspect of the sport. If that's the case, try to make a deal with her. Maybe "our team will try to do this in the best possible way, and if we can do this successfully, can you let us to basic stunting?" But talk to her about this in private. Also, your team may not be ready to do any stunting. The majority of my team is capable of stunting, but there is one girl that I do not trust to stunt. My team didn't have a try-outs, anyone could join because I needed a team. There isn't enough interest in that school to have a tryouts. So I have some girls that need to work on other, more basic things before they stunt.
Long story short, talk to your coach in private and maturely ask her why she won't let you guys stunt. Then ask her if there's anything your team can do to prove to her that you're ready to learn how to stunt. If she says no, then end the conversation, finish out the season, and do allstars. :)