If at 14 she hasn't lost that confidence yet, it is likely, imo, she won't.
However, if she wanes, be prepared to give her opportunities to excel again. Help her develop leadership and initiative by taking on a project where she is her only limitation...ie start a book club that includes teens and adults...start a fund raising project for a local need (a kid here is raising funds for a police bike patrol)...build a deck (seriously)...etc. If she has some area where she is allowed to excel, she should be able to carry that confidence through the challenges of public school, imo.
