I can understand not wanting to put a pet through chemo. Frankly, if it were me, I would not opt for chemo, regardless. If it were me, I would implement A Natural Anti-Cancer Protocol and pray a lot. And you know, vets and doctors can be wrong. We have a lady in our Oleandersoup forum who's dad with pancreatic cancer was given two months to live. She implement the Natural Anti-Cancer Protocol for humans in full force and effect and a year later he is alive. Not cancer free mind you, but he is up and about and playing a round of golf each day. So what I am saying is, don't give up. I merely gave you a couple of options.
My prayers go with your sister and her precious furkid.