I understand what you're going through completley. This is kind of the opposite, but when my friend hooked
up with an athiest guy, she began to doubt her faith too. Let me assure you, however, that a bond you make with God is a strong one. You cannot break it unless it is the ULTIMATE circumstance (meaning, you're REALLY REALLY angry). A lost relationship is not gonna make her lose her spiritual promise. God is more attached than that. In the meantime, be sure to be there to support her. Remind her of how good God is. With my friend, we had a three person bible study(herself, myself, and an additional friend). When she usually just went for a Starbucks Hot Chocolate and some gossip, she heard a lot about God's great promises. I know 30 mins. b4 school might not seem like much, but trust me, they go a long way. Those words will be popping up in her head until she goes to sleep that night. Lastly, (sorry, I nkow this is really long), every Christian doubts God every once in a while. We are human, we tend to wander and fall astray, why else would we need a sheperd to guide us? Keep praying for her and nuge her in the right direction, and God will do the rest of the work
.