I would also make sure she has medical clearance to workout. The intensity and the type of training program it depends on her fitness level and other existing limitations (if present). Usually lower impact movements as well as lower HR intensity should be some of the things you need to keep in mind....
I agree with Karin. This person is never going to be happy no matter what you do or offer him, so it's best to let him go. And if you try to give him suggestions of other places he might blame you again if things don't workout for him.
I agree with the others. She will need to be re-evaluated by her doctor to rule out any hidden issues. Then you can decide which approach to take. He pain could be very much related to the surgery she had on her intestines.
Not much information is provided in order to give you a better answer. The calories burned on the treadmill are not always 100% accurate. And I agree with the others who suggested for you to keep track of your BF%, not just your weight.