Welcome!
You are in quite a predicament! I'm sure she is a very wonderful woman. The problem as you have already surmised is her being born into the cult, plus the Mexican culture is VERY family oriented. Both these compounded, makes for a very confused girl. It is my guess that unless you convert, you will not be welcome in her parent's home. Which is evident that she it TRYING to figure out how to introduce you to them. This is very difficult. Even if she leaves now, there's no guaranty she will not be overcome with guilt after having children or having a family member die. Even now she may be forced to pick between her family and you, which of course will lead to a very sad girlfriend/wife.
Tread lightly, I'd say.
Good Luck,
Bryan
Have You Seen My mother