Cockatiel tumor

I have a 12 year old cockatiel that has her 3rd tumor on her bottom. The first one was when she was 5, next one was 9 and now she has another one. She is such a good bird and so loving. If I get out of her sight she will pop off her perch and follow me and just wants me to hold her under my chin and pet her.

Problem is the money and when do we stop having these removed. This operation will cost over 400.00 and we just don't have it and would have to borrow if family member would even do it. The vet has a plan where they would hold the check for 2 weeks and that still doesn't work. I spoke to them and this is the only way.

Other than this tumor (she starting to make it bleed) she is healthy and acts like a 3 year old child.

How do you tell when we need to give up and have her put down which will break my heart.