What is it exactly you're struggeling with?
What levels are in your training group?
Sounds like a tough situation for you, but really, you shouldn't listen to your teammate who's a level 8 for the third year - of course she has the skills and I guess she's just worried and insecure if your coach wants to move you to L9 but hasn't moved her for a couple of years now. She probably wants to prove her standing and show the coach that she's just as good and should be moved up as well.
Also with about your coach - obviously believes you can do it, otherwise you wouldn't be training that level. Relax. Whatever he does to make you feel insecure might be his coaching style - maybe he believes it to be motivating?
Try talking to him in a calm manner,... that you are not sure if you can do it and that sometimes you need more reassurance that you can.
Last but not least - you're in it for yourself. If you feel you've given it a good try, than you are always good enough. Gymnastics is a tough sport, and there's a limit for everyone. The higher levels take work, and you have to decide for yourself if it's worth the stress. Try to enjoy the time in the gym and not think about "failing" all the time.
If I were you, I'd stay L8 for now but talk to the coach about your worries. And just try to enjoy gymnastics,.. get away from the pressure you put on yourself