I used to do a competitive sport as a child (think ice-skating, it wasn't but similar pressures). I know my mum was sometimes looked on as pushy just for providing me with the opportunities to do what I needed and wanted to do- for example taking me to train before school and letting me have days off school to go to competitions.
I have never, ever regreted that I only did that one sport and wasn't an 'all-rounder'. Tbh, when the time came I also think it got me into Oxford because they were as interested in my sporting achievements as they were my A Level grades.
I wouldn't limit your daughter's chance to achieve what she wants to because of other people's opinions- just make sure the impetus to dance is coming from her and let her do it at the level she wants to.
Is it ballet? You could just get her into the Royal Ballet School and let them tell her how many classes she needs to do??
not sure yet, still figuring it out. CURRENTLY I take the view that DS can do more of his chosen sport in holidays but on school nights I limit it and don't let him do anything that will result in a very late bedtime. BUT DS is rather younger than your DD.