Urgent situation with large mammary tumor

My amazing little 16-year old orange tabby Tigger has had a large lump develop quickly into an open, rotting tumor. The first clinic I went to suggested immediate removal of this awful thing, saying it's most likely mammary cancer and although there are other little tumors popping up and it won't buy that much time, keeping this thing certainly won't help it. I went with the original owner of my little friend to her (the lady's) vet and he insisted that removing this tumor would put the cat, at her old age, through too much for what might as well be a cosmetic issue.

I'm torn. The person paying for the surgery is the owner before me, and she will only pay for it through her vet. That is, if I give the say so. They made it pretty clear that I would be the bad person in this situation to have it removed. The first people I went to suggested it would be worse to just leave a rotting mass as is, I mean it really isn't making it any better. At least she could go outside happily again this way. She is a strong, fiesty little thing even at this old age. I felt somehow confident that even though this is a big surgery, she'd make it through and recover long enough to have some more adventures in her life before the other tumors inevitably progressed into her lungs, as this diseases apparently goes. It's horrible, irreversible, and I feel tormented by what is happening to my best little friend in the world. She's so amazing, funny, unique, and loving, and I never dreamed something like could ever happen to her. She's been with me through so much. 

I apologize for the emotional parts, it's obviously an emotional time. On a final note, the previous owner said that Tigger's mother died last year of the same thing, two weeks after her operation. However, this operation was at a different, more local clinic, where it sounded like it was badly and sloppily done, and they wouldn't even address it.

I am clueless and have no idea what to do. The operation would be covered, but only if it's by the vet who suggests it's better to leave it alone. I cannot imagine her lasting very long at all this way... Any advice anyone here can offer would be appreciated. I cannot stop panicking.

What a difficult situation!   I'm glad though that you have the option to proceed with the surgery if you choose - even if nobody else thinks it's worth it.....

If it were me, I would choose to go ahead and have the surgery (as long as we could work it out financially - and I would do whatever was in my power to do to try and find a way).    I agree with you - no good can come of having an open, rotting tumor just hanging out on your body - who wouldn't want to be rid of it??

And, if I'm understanding correctly, it sounds like some kind of hereditary disease, and other tumors are likely to form - then even if the surgery did  end up taking her life, as awful as that would be, at least she would be saved from her inevitable future suffering from this disease, and you would feel confident that you did everything you could up to that point to save her....and didn't let her just linger around with an open tumor (I'm pretty sure she wouldn't want that).   

Good luck to you guys - I hope that a decision can be reached that everyone feels good about