We have been through this. DD has just finished year 11 but we spent a slightly concerning few months a while back when she announced she wanted to study art elsewhere. We had several discussions as to why and it partially comes from a desire to exert her own independence and partially the feeling that the school was not focused on the "right" sort of art. Engaging the art teacher and many discussions talking about further stages in studying art allowed her to rethink the decision and stay at WGGS but with a view to do an art foundation before finalising the degree choice. She has decided on Art History, Fine Art, English and either Maths or Music at A level, result dependent.
Be open with DD and don't be afraid to talk to the school, they are very keen on students staying especially if they are able.