I’m so sorry for you and your little kitty, and have been through this myself with two kitties who had cancer. I’ve read some of the posts and seen good advice offered. In case no one else mentions. a high white cell count also indicates infection, and sometimes we do need a second opinion from another vet clinic or hospital, just as for ourselves.
I would never put a kitty through chemo, but that’s me. It would poison her little body so badly. My older cat, who had a squamas (?) cell sarcoma, did well until she was nearly 20, while also battling kidney disease and hypertention. We were so in tune, I relied on her to let me know when she didn’t want to go on, and she did, unmistakeably. But my younger kitty, my last baby, had a brain tumor - long time to diagnose, as she was 18 and I wouldn’t put her through anesthesia for diagnostic, surgery, or anything else. She went blind before she was 19 but lived another year, also to almost 20. Close as we were, she wouldn’t tell me she wanted to go (and by the way, there is nothing really safe for pain for cats, except morphine - strange! - which vets won’t prescribe as a rule.) My baby clung to me and just refused to give up. But then one day she had a terrible seizure, and I took her to be put to sleep that very day. I waited too long, and her quality of life had deteriorated badly, but because she wouldn’t give up, neither would I. I know now that was a mistake and I had needed to give up for her - so don’t let that happen, but be guided by your concern for her above all, if you can. It’s very hard. God bless you both.