I'm so glad that Emma has had the surgery and is 'trying' to go in the box. What a fighter she is! I think Krazyaboutkatz idea to cover the cage with a sheet would really help. Even if it was just over 3/4 of the cage. She probably needs to feel cozy and a sheet would make it more like a den for her. Or maybe you could put an old sheet in the cage for her in a pile to curl up on that could be tossed in the wash each night. Might make her feel more like resting and be less anxious.
I think it's great that your MIL and family have given her this chance and I hope she will begin to be able to urinate and deficate on her own one day soon. I once had a ferret years ago that got caught between a loft bed and the wall when I was at work. When I got home I found him and his front right leg was limp and not moving. I rushed him to the vet and he was there for a week or more and they said there was nothing that could be done and that the leg was useless and I should have it amputated. I just felt that I couldn't rush into it and asked if I could take him and try some physical therapy. They thought it was pointless but sent him home. Within 3 weeks of moving his leg in circular motions he regained full use of this leg. I know that it is not the same thing but I pray that Emma will be able to regain her ability to use the box on her own. She sure seems to keep trying which is so encouraging. This might sound very silly but I'm wondering if you were to take a scooper and shovel it around in her box making sounds that she is familiar with might create an 'urge' for her to go? Kind of like a Pavlovian response? lol This thought came to me because one of my cats does this. Every single time I begin to scoop his box, here comes George and he NEEDS to get into that box ASAP! Maybe if you did that a couple of times each day it might help her to keep trying.