Yes, I know a lot–I went there =)
The girls are a mix. About non Jewish music, most girls probably start out with it, and many (like me!) stop listening over the year. There isn’t peer pressure to listen to music; I found that people respected me, after all, seminary is a place to grow! But your daughter will need to be confident in her decision.
I made sure to find a good group of friends–normal, fun girls who were frum and looking to grow, and grow we did!!
There is a mix, just as there is in every seminary. Some girls totally “flip out,” and become frummer than BJJ girls, and some girls grow in their own, less obvious way. As long as your daughter finds herself a group of good girls who are not interested in partying, she will stand to gain from the amazing staff (I can’t stress how unbelieveable the teachers rebbeim and mechanchot are!!!) and the wonderful girls that go.
But your daughter has to decide if she thinks she can be confident in her decision to grow, and if she thinks she can be mature enough to find herself a good group of friends.