Stop and think a moment. Ask yourself why she doesn't like what your youth pastor is doing, then observe what he/she is doing yourself. Then openly and calmly ask her what is bothering her about your youth pastor. You may find that it may be for your own good and that there is something that is bothering her about the way he/she does things for a specific reason.
But if you see nothing wrong with what your youth pastor is doing, then tell her. And then tell her that you really like being there at the church. But also listen to why she wants to leave. It may be a matter that only she can understand because she is older, more experienced, and knows what can do harm to growing teenagers in a church environment if things are done in a certain way.
Basically, you both need to be open with each other and find out what's going on. And I'm with everyone else, we need more information.