Have you tried sitting down with her and a map, to map out a route that she will feel comfortable with?
Or you can just ask her why.
Or watch some youtube videos and get her bike working again, get her a helmet, and ride the route to college with her so she can see how it is and see how you will do in traffic. This could also ease her mind about you going out riding with friends, maybe. It'll also give you two some bonding time.