Okay, you asked for honest opinions, so I'll give you mine--I would wait a year. It sounds like your DD does plenty and enjoys her current schedule. Let me offer my perspective, from a few years down the road. DD13 (yesterday!) has been dancing since she was 3. She would love to dance professionally as a career. My big problem with her is, she loves many, many activities, and has a tough time choosing, so she wants to do them all. They all have value (Scouts has service, Odyssey of the Mind is creativity, etc.). But it gets to be A LOT. Here are the things she did this past year: 7 dance classes, cross country, track, OM, scouting, NJHS, Advanced Math, Young Scholars (gifted program--one day per week, instead of her regular classes), newspaper, poetry pocket, trumpet (band and a solo), theater, and probably a couple things I've forgotten. Through the years she's dropped gymnastics, piano, karate, soccer, and again, probably a few other things.
She just finished 7th grade, and this is the first year I've seen her have to really work to keep up her grades. I think missing one day a week hurt her, plus all the after school stuff. She complains about not having free time, but won't drop anything! It can be difficult to help her find balance, but it's my job to oversee and make sure she doesn't get overwhelmed. You've got a long road ahead of you in dance, and pacing is wise. Especially in a field with so many potential injuries.
So, since she's not begging for a solo, I would skip it for now. If she asks and seems very interested, maybe it's something you can offer her "Well, if you do well in school and keep your grades up, we can do one next year." YOu also have to be careful of focusing every free second the family has, on just one child. I'm sure your little one doesn't have a ton of activities at this stage, but will, someday. I have 4, and Dh and I frequently feel like 2 cuckoos popping out of the same clock, with our running around! Sure, both my girls are dancers, but totally different classes, and DD5 isn't showing the same "thirst" for dance at this stage (begging for violin lessons, but that's a different thread!). So, beware of making the schedule and family focused only on the oldest--not saying you are, just that it can happen.
Anyway, sorry for the novel--I hope it helped. BTW, if she is begging for the solo, and if she keeps her grades up, I would let her do it next time, if she were my kid.