Most Helpful Girl
If they broke up cuz of distance and nothing else it should be very clear to you that there are huge chance that she's not over him yet, so if he's back, they can go back together.
I think it was wrong of you to allow her to talk to him, because he's an ex and is supposed to stay an ex.. no contact whatsoever. Now that u told her it's ok, she's gonna take it as an opportunity to talk to him more and more. Which in turn can gradually make her change her decision from you to him.
And for the last part, her blaming you for every little thing, that already is a red flag for a relationship that's not gonna go well. Also deciding to get married that early is also something that's really unnecessary.