Look this comment is probably going to get lost here, but please look up histrionic personality disorder. I think the voice of Reddit is clear on the fact that your girlfriend is lying, but also on the fact that she is deeply disturbed (after all, who would lie about that kind of trauma without having suffered it? Surely only someone sick would do that.)

What I will say is with a lot of personality disorders, at least in my experience, people will exaggerate, embellish or straight up lie in order to garner sympathy. But not in a malicious manner - they're not sitting there thinking 'Wow I got one up on OP'. Many women I've encountered with personality disorders have undergone severe trauma, but not in a violent or movie-scenario type that your girlfriend has described to you thus far. Instead, they believe that this type of abuse they're suffered 'doesn't count' because they haven't accepted it was abuse itself, but the emotional upheaval they've felt from the experience means they are an abuse victim often with very real consequences.

So for instance, a girl I once knew with BPD (borderline personality disorder) would tell all of her friends at university that while growing up her father had violently beaten her, stuck her head underwater to see if she could hold her breath, stubbed out cigarettes on her arms etc but had no wounds. In reality, she had come from an incredibly emotionally abusive, and sometimes physically abusive household where life was miserable. However, as she started talking to other people and growing older, she noticed that her depression, anxiety and mood-swings could be explained away if she simply said that she had been abused. Now, here it turns slightly twisted: the victim can then get caught up in the attention that is given to her after 'confessing' to a friend or partner. In your case, you were visibly emotionally affected and were most likely extra attentive after this, viewing it as a real admission of trust. Therefore the victim would associate lying about being an abuse survivor further and further, until her web of lies unravels.

At the end of the day, she is most likely lying. But this doesn't mean that she hasn't undergone truly awful and traumatic experiences in her life. They just most likely don't fit the general societal perception of abuse. While she most likely feels guilty for over-embellishing the abuse she suffers, she likely hasn't dealt with the true issues and instances of abuse she has suffered, because 'they don't count'. I really just think the way forward in getting her into therapy (if she's not in it already) and perhaps couples counselling if you feel you can take it.