I'll share a bit of my story with you privately, since it's off-topic in /r/Christian/. It may help you to understand her more, particularly if she's done her homework on this.
I was raised in a very Catholic area, but not a Catholic. It impressed on me the need for God in my life, so I became a born-again Christian at 18 in a Southern Baptist church. I was very zealous for my faith; I've led Bible studies, I've done street evangelism, I've been involved in church plants, and I was really into apologetics. I also put myself through evangelical Bible college, and have a BS in pre-seminary work.
For 27 years I was an evangelical, and trusting God for everything. But, along the way, I had to slowly admit that God was not as responsive as I had hoped he would be. In fact, I couldn't honestly say that my "relationship" with God had made any significant difference in my life.
Tired and frustrated, I guess I wanted answers, and didn't really care if they were the "wrong" answers according to my evangelical peers. I had always studied science from the perspective of Christian apologists, who, of course, tossed out any scientific ideas that were in conflict with a literal reading of the Bible. I read this book on flood geology; the author seemed like he was trying to be very respectful of the Bible, but the evidence against a worldwide flood is pretty solid, and this is the majority opinion of geologists around the world.
I started studying evolution, and realized that the volume of evidence of favor for it makes it a slam dunk. Young Earth Creationists had always made it seem fragmentary and shady, when the reality is completely different. And again, it is the majority opinion of scientists around the world.
Then I started studying about the Pentateuch, which are the first five books of the Bible. It's well known by scholars that each of the books (except Deuteronomy) has been heavily edited; even conservative Bible scholars know this -- they just don't talk about it. Historians, archaeologists, and Egyptologists also know that the evidence is against the Jews ever having been slaves in Egypt. Nor was there a Moses. Nor was there an exodus. Nor was there a meeting with God on a mountain in the desert. Nor was there a handing down of the Law. Nor was there an invasion of Canaan, as described by the Bible. Once again -- this is the majority opinion of scholars (even Bible scholars) around the world. This video provides a good summation of what most Bible scholars know, but churches won't talk about.
Here's the real issue from the last paragraph -- if Moses wasn't real and God never told the Jews to sacrifice animals to cleanse the sins of the Jewish people, then why did Jesus die on the cross? Because it surely wasn't to be a sacrificial lamb. And that is the central idea of the New Testament.
The first five books of the Bible are foundational to everything else that happens in the next 61 books.
The actual collapse of my faith was quite swift; it took about two weeks, from start to finish, because I was just devouring scholarly information about the Bible. I realized that the Bible was not a reliable document at all; and if the Bible wasn't reliable, then what is my faith in Jesus based on? It had been based on the stories of the Bible.
Anyway, this is a lot to take in, I'm sure. Do a Google search on the historicity of the Exodus, and see what you come up with. Believers who are trying to come to grips with it are trying to argue that it may have been much smaller than the Bible describes, to the point that it could have happened without leaving an evidence trail -- but then we're at the same problem of the Bible account being unreliable.
I apologize for the length, but I'll give you one more resource: free Yale University Online Courses about the Bible. This is the most prestigious university in the US; what do they say about the Bible?
Anyway, good luck to you and your girlfriend, and feel free to message me if you want to talk more.