Just because Monica is hypothetically the eponymous gold digger, that doesn't mean she was actually digging for gold. Donald is not a reliable narrator. We don't know when her affair would have happened or how she feels about it now. We certainly can't assume Donald told Elaine the truth about Monica making a pass at him just because we learned she slept with him; admitting he instigated it wouldn't exactly inspire Elaine to trust him. It's even possible, as
Ramen- said, that Donald may have named her an heir to stir shit up posthumously. Monica being named in the will doesn't automatically make her a villain.
The only that happens is everything about Monica has an a laughably impractical con from day one. If she's the one Greg warned us about and has been orchestrating events for years, then yes, there will be drama. There had also be one hell of an explanation for how that makes a lick of sense given what we know of Monica, the girls, Donald, and the email that kicked this whole thing off.