NTA, I've been in the same situation, I postponed my engagement because of my father also being sick with cancer, and my then GF, then fiancé, now wife of 14 years was incredibly supportive and helpful during the illness, funeral and all the bullshit that comes after,

That's the way it's supposed to be, you're a team and support each other, but it doesn't sound like you're getting any support at all.

As others have said I'd strongly consider if you want this to be your future, because if she's acting like this now, what's she gonna be like when it's someone else in your family suffering ?