I wouldn't stress about this. If you haven't already, ask her how you should recognize those days.

I find that I don't often want to talk about my messed up parents unless they do something that irritates me or I happen to remember something crappy they did years ago-- so, yeah, there is a good chance that she just doesn't want to talk about it. I like swapping stories with someone else who had parents like mine, but otherwise, it's just not something I want to talk about-- but that's me, not your gf, so I would ask her