I am not familiar with either school but I am the owner of a Yr 9.
Before you jump to the conclusion to jump, have you considered these questions:
How has your dd's academic performance been in Yrs 7 and 8? Is she keeping up with her peers, have the school expressed any concern that she is struggling, do her effort grades match up to her academic grades? i.e is she clever but lazy, or genuinely struggling and the pressure is making her anxious?
Have you talked to the school - her tutor of head of year, about her unhappiness? can they shed any light on her relationships with other girls, or suggest ant strategies to make her feel happier? Keep a look out for people being mean to her, make sure she is not in groups with certain girls etc?
Yr 9 girls are famous for being in a difficult moment, you need to be sure that her problems really would be addressed rather than just shunted to a new location.
Finally, you might get more response about the particular schools if you start a thread asking for views and experiences of the two schools, and name them in the title to attract those who know.
I hope whatever happens things work out for your dd.