Taking on that much debt would be a pain. But that pain would be dwarfed by the pain you’d eventually be subject to by taking on a spouse with marginal (or worse) character, along with clearly bad in-laws.
I’m not saying she has bad character. I’m saying it’s certainly possible, and that I’d be way more worried about that than about the money.
Obviously I don’t know any more about it than what I’ve read here, but “I didn’t know” sounds like bs from where I’m sitting.
Even if she didn’t know, it seems like she should have. My guess is that she’s know for a long time that her mom’s a scammer, but either went along because she (your ex or fiancee or whatever she is) is also a scammer or because she was too weak to stand up to pressure from her mom. Either way, not marriage material.
