Well....you will have to start from scratch. But don't worry, she will respond. Sounds like she was well on her way before her people dropped the ball.. I will give you a way that is very restrictive..for YOU and your fiancée. But it works. She needs to be leashed at all times in the house. Attached to a human, that will be watching her every move.
Out every hour to potty AND after eating and playing. Before going in the crate AND immediately after. Try taking her to the same area outside. They begin to know that's the place.
No Roaming Freely..
On a leash at all times. If the human needs a break, take her out to potty (the pup..lol) and immediately in the crate. When she comes out of the crate, immediately outside to potty, then back on the leash.
If you see any signals she might be thinking about going, a gentle tug on her leash..your NO word and take her out immediately!
High praise when she goes in correct place.
Keep crate area small, no bigger than needed for her to stand up and turn around.
Yes..it is a difficult thing..tethering yourself to a pup..but it works. You will be amazed at what you were missing.