I'm sorry this happened to your cat. She's at an age that surgery is harder to do and very expensive, you have to weigh the odds of the outcome versus letting her live her life w/o surgery. If she is eating and happy and it's not bothering her then it's going to be your choice. My neighbor was just in the hospital for a heart issue, her aortic pump is not working right meaning open heart surgery. She is 89 just lost her hubby back in Jan, and very frail. The surgery was explained to her and she said no I want to enjoy the time I have left to be able to not have pain of that surgery, to not be restricted healing in bed, and I'm not going to do it. I think if I were in her shoes I wouldn't either. My first cat wound up dying of kidney failure due to heart condition, he was 16, I didn't want to do the heart surgery as he probably wouldn't have survived it, he was eating and happy until the kidney problems started then I did have to put him to sleep. When it gets painful and hard for her to move around and do the things she needs to do like eat, sleep, and use the litter pan it's time to do something. It's totally up to you, it might be with the other lumps it is spreading. Has she been to the vet or did you just call and consult? I'd at least take her in for an exam and maybe a needle biopsy, and see what they say before I made the choice.
I am so sorry to read this, does very much sound like mammary cancer, however PLEASE have kitty checked over by a Vet asap just to be sure,
IMO at her age and what sounds like advanced stage of the tumors it wouldn't be possible to effectively treat her.
She will soon need a source of good pain control though and I sure hope you are going to follow through with this with a your Vet, I'm sure you won't allow your kitty to suffer.
With guidance and pain control from a good Vet you can hopefully keep kitty with you for a few more months....when they stop wanting to eat as usual its a pretty fair indication of pain, but this isn't always the case...she could well be suffer now, thats why its so important to consult with a Vet.
again I'm sorry. please continue to post and keep us updated on kitty...♥
I know folks who have been through this with their kitties will have better advice.
However, if kitty seems to still be enjoying life and is in no pain, keep the area as clean and dry as possible. Keep treating her with the kindness and affection you must have been doing for her to make it to 16.
Other than that, you'll know when it is time for kitty to make the final vet visit, which is something to keep in the back of your mind.
Take care, of you and kitty. =)