Haven't Felt Like Crocheting. Worried About My Dog.

My dog Nikki who is going on 14 has a tumor on her breast. The vet told me a couple of months ago she would need surgery that would cost over $500. (which i don't have) She (the vet) said she does believe it is cancer given her age. Keeshounds avg lifespan is about 15. I had her mom until age 13, and her father until age 12. She also has arthritis pretty bad in her back that i have to give her pain killers for when it flares up. The past couple of days, i noticed she's not putting much weight on her back right leg, and the tumor has gotten bigger. I have a call into the vet. She 's not crying in pain, and is eating, drinking etc. Last night and this morning i gave her the pain meds just in case since she's kinda just laying around. It's so hard. I don't want to see her suffer (if she is) and i can't see putting her through a surgery that may not "cure " her. I just don't know what to do at this point. I'm going to explain this to the vet. I would hope they have her best interest at heart and not just try to make money. My nerves are shot over this. Part of me says there's hope, the other says it's probably her time. No more dogs after her, i'm done.