My daughter is also 7, and moving up faster than most of her friends. She and one other girl her age are basically doing the same thing your daughter is, except they will be competing once at L5, then moving (probably) to L6. At least they have each other, but they, too, will be leaving most of their buddies behind. On the L6 team at our gym, there will be these 2 who are going into third grade, then 2 fifth graders, then a 7th and an 8th grader.
First, let me say that the older girls are basically good kids. I certainly am not afraid to have them working together, but I know she will encounter that pre-teen/tean attitude. My dd's friend has already had a little bit of trouble with the older girls. She describes them as "snotty". Basically, they will say things like "You're such a baby" if they think the younger ones are getting special treatment or asking for special things. Or they will walk away from the younger ones saying "You're too little to hear this." And it's not always WHAT they say as much as HOW they say it...with attitude.
Aside from just being a difficult age (anyone remember jr high fondly??) it's also perfectly understandable that older girls will be jealous of younger ones at the same level. Who wouldn't be, right? They may resent it when our daughters make tricks look easy, especially if it's a trick they are struggling with.
I've warned my daughter than some girls can be a little mean, sometimes without even meaning to. But I've also told her that sometimes they are mean on purpose. And I've advised her to just ignore as much as she can, unless it is really hurtful or gets out of hand. But the point I've tried to really get across to her is to not be braggy about how well she is doing. Self-confidence & pride in your work is awesome, but I've tried to teach her how to express those things without putting others down at the same time.
And the time my friend's dd had a problem with the older girls, my friend ended up telling her daughter that they were all a little bit to blame. In this particular situation, the coach should have put a stop to her daughter's questions, AND the older girls should have left it up to the coach and not gotten involved, AND the child herself should also have known better.
I'm never one to say that a child deserved being treated badly, but at the same time, I want my daughter to understand that she often contributes to the problem. Things are rarely completely one-sided.
Ok, that is a much longer answer than I intended!! But I hope it helps. Incidently, the girls we are more worried about are the girls they are leaving behind. A few of those girls did 2 years on L4 and are barely moving to L5, but our girls are now passing them by. I think those are the girls who are more likely to be mean to our girls. We've already had a little bit of that because our girls did TOPs this year and the others weren't invited to.
Good luck! And give your dd our congratulations on her progress!