If her chance of imminent death from cancer is high enough they WILL do surgery right now. They will be explicit that the surgery could kill her but so will the cancer so...her choice. Physicians are rather risk averse, though, so, if its spread is slow enough they may buy time with non surgical therapies while making her lose weight then do surgery. Pre-cancerous cells or stage 4 cancer, either way that uterus will need to go. Keep in mind that she has a lot of adipose tissue where all those toxic chemicals she's going to be exposed to can linger...she'll have side effects x 100 and be at risk of other cancers down the road.Can she even get surgery at her current weight?
If she tries to pull the ole "I know what's best for me", they'll give her some supportive therapies like pain meds BUT they aren't going to waste time treating a non-compliant patient.