Dr Larry or anyone? Tumor Question?

I adopted a small starving (*very* thin, 3.5 lbs or so) Calico last fall. When she went for her checkup prior to coming in the house, her abdomen was hard and distended, pee & gums orangey, and her bilirubin and another lab value were way off. They told me she had a pancreatic tumor (likely) could not have anesthesia, and sent her home telling me she would become very ill very quickly and would not live long. They did try to help me arrange for a lo-cost ultrasound, but it fell thru. I brought the the cat home to make her comfy as I could for her remaining time.

But she really fooled us! 8 months ago her hard abdomen softened and went down. Her activity level is very high. She has never had an episode of diarrhea and only 1 vomiting incident (but another cat also vomited the same canned food.) She is now at a stable weight of 5lbs,drinks & eats very well (esp poultry breast) and plays hard and bosses my older much larger neutered boys. She has been more or less in heat since October, and we feel like she really needs to be spayed before we all go 'round the bend. We seriously love the teeny girl and don't want to risk her, though. How can we know if she might be fit for surgery ? We're on SS and have to be very careful with our cat-care budget.