Wolf, I can understand why you are confused. I'm only reading what you post here, I don't actually know her or you beyond what you post. So I can't say 100% that she is a scammer, but I definitely get that impression. Here is what I think, again with the understanding that I have limited knowledge of your situation:
I think your GF is trying to entrap you. She may be a predator masquerading as a damsel in distress. Tricks you into letting her move in. Plays Suzie Homemaker to cement her position once there. INTENTIONALLY gets pregnant to lock in her spot. Guilt-trips you that she has no place else to go and no one else to turn to, and what kind of evil man would turn a poor, innocent, pregnant girl out onto the streets. Now that she's established herself there, now comes the next phase. Threats, lies, gaslighting, manipulation, withholding of sex and house duties in order to get what she wants. The very definition of gaslighting is "manipulate someone by psychological means into questioning their own sanity", and that is how you are basically describing your state-of-mind right now, isn't it. She's preying on your "nice guy" tendencies, using that against you to keep her spot in the house long enough to establish residency. Ultimately she wants marriage so she has legal recourse to half your property plus alimony and child support. Once you are married the really harsh treatment will begin, it will make what you are going through now look like a vacation in Cabo.
I've actually seen a few situations like this involving young, predatory women.
Here is the thing Wolf, whether she's a scammer or whether she's just an innocent young lady going through some things, EITHER WAY the BEST thing to do is get her out of your house so the two of you can sort out your relationship with the benefit of some distance from each other. Once she's out and a little time has passed I think you'll get your head straight and sort out if she's a scammer or not.
Also I'm not sure I've clearly stated this but a paternity test is a must. There was a show about one of these scammers who moved in with a guy and coerced him into unprotected sex while also sleeping with her "real" boyfriend, intentionally trying to get pregnant (which she did) so that the target would think it was his and "do the right thing" and marry her. Don't assume anything.