So far as we know, she has no issues other than being fat and having horrible taste in men. I doubt Greg is marrying for anything but selfish reasons, though, as he chose to be a babydaddy instead of a father and to act like a stereotype of one of his own criminal clients. He didn't even consider his firstborn worth marrying for and chose to be a deadbeat dad sperm donor piece of shit instead.
So he's marrying her for some nefarious reason. And there must be something wrong with her too, just because of the fact of marrying a piece of shit like this, although so far I'm going to assume she's the duped, innocent party and hope that she escapes without him inserting his debt tentacles into her far enough to evade his own debts, the most obvious reason for him to marry like this.