I'm sorry, but I don't think you'll have a year. We lost one of ours to a very fast growing tumor on the liver. He was feeling 'off' at the start of June, I took him in & they checked him over. Blood tests showed two liver enzymes were going though the roof, all the rest was normal. His X-ray showed a small spot about 1/4" large on the liver.
Three weeks later he was in terrible pain, I'd felt the mass 4 days prior to our taking him in for euthenasia, even on antibiotics and a few other things we tried the tumor was growing at the rate of an inch a week. There was no saving him, it was devestating.
My other cat has a chicken egg sized lump on his liver which is NOT growing, and all his blood tests show he's stable, the readings are in the low end on some, upper end on others, but still within 'safe' parameters. He's not got issues with anything else--weight is stable, kidneys functioning, etc, even at 18 years of age. With him we might be able to have 2 more years, but if it takes a turn, things happen fast.
The fact your cat has significant changes is not good. I'm so sorry. Enjoy her while she's with you.