One cutesy name for this behaviour is 'zombie dating'. This happens when someone disappears on you but then pops up again as if nothing has happened and makes comments on your socials etc. It's annoying, and confusing, but can be harmless if that's as far as they go.
If she managed to get you—not even a close friend—to let her move in, this woman is resourceful. I wouldn't be so sure at all that she would end up in a shelter.
Weddings should be joyous celebrations, yet complex family dynamics can turn them into battlegrounds. It's essential to set boundaries to preserve peace on your special day.