Hi zoo, I am no expert but both my DDs dance at the local dance school. We are very lucky that our town has a very well regarded dance school where the emphasis is on fun at first but also students go on to have professional dance careers. They train out of a church hall type place so I think the fancy studio doesn’t necessarily mean a better school. However it might mean nicer floors and mirrors making technique easier to correct.
A few ideas...
Could you ask the open ballet class if they recommend anywhere?
Can you try out a few places and see which one fits her best? No decent school should mind students trying a class out. In any sport I have ever been involved in, prospective students have been welcome to try a class. Anywhere wanting you to pay for a course of lessons without trying them is a massive red flag to me.
If they all seem roughly the same then maybe pick the more convenient one.
If you are taking siblings then what is the waiting / local area like?
Are you on Facebook? If so go onto your local pages and ask for recommendations. Word of mouth is the best way I think to find somewhere.
Re. the teacher. I initially found DDs’ teacher a it strict. We had moved from a super relaxed dance school. But she is really not and she really really cares for the students. I think that is the most important thing, do they seem caring? And do the senior students look happy. Again a red flag if they all look miserable.
You may not be getting many replies to enquiries if the dance schools are off for the summer.
If there is a local dancewear shop near you go in and have a chat.
Tldr: try a few out, ask for local recommendations, look at senior students to see if they look happy.
Hopefully others will be along with tips too.