I don't know anything about the book in question, but I feel that she might be more comfortable sexually if she gave it a little "me" time. It's my guess that she probably hasn't experienced a whole lot in the way of masturbation. One of the best ways to figure out what you like sexually is to figure it out for yourself, get comfortable with sexuality and what your body does on your own, and then share those discoveries once she feels comfortable with them on her own. That way, there's no intimidation, there's no pressure. If she's comfortable with her sexuality when alone, she'll probably be a lot more comfortable sharing that sexuality with someone else.

Girls are raised not to masturbate, while boys are raised being told it's normal. I think it might be a helpful thing to encourage.