Please do try to get her some medical attention. At least a needle-biopsy of the tumour, so that you will know what you are facing, and some antiseptics and a dressing for the poor girl's open wound.
If this is a benign tumour, and could be removed easily she may have quite a few years still left in her. If it's cancer, then radical surgery often does provide a cure. My own dog had a half breast strip at age 13-14 and came through it very well indeed. In the vet's opinion, the breast cancer was cured by surgery. Unfortunately she passed away some time later from something completely unconnected to her breast tumours or the surgery.
Try anything you can think of to raise the money. One good thing about ebay is it can take only 10 days to raise funds from sales, and sometimes even 7 days.
Otherwise care credit is a thought? Borrowing from the bank or family (to pay back weekly or monthly)? A Facebook page with a link to GoFundMe? Sell your car and take the bus instead? Sell your computer (etc)....I don't know
Well, one thing is sure: you cannot continue toallow her to injure herself further. If you have no means of paying a vet, I am sorry to say this, but it may be time for you to send her to heaven - 13 years is a LONG dog-life.
Agree with tony. This is not something that should be left unchecked. It could even be Cancer and your dog is obviously in pain. Left untreated, an infection could become systemic.
Please find a way to go to the Vet. Your Vet may take Care Credit and coukd tell you if you qualify. Maybe try your local ASPCA.
There is no other remedy here other than going to a vet. This needs professional and urgent attention. At the very least she will probably need antibiotics, otherwise the wound will become severely and painfully infected. Sell possessions, ask friends or relatives for help or approach a local animal charity. Alternatively, contact the vet and ask if you can pay by installments.
There is no problem that doesn't have a solution ... you just need to find a way around it. Your dog's health and wellbeing is your direct responsibility and there is always help available, but you need to look for it and keep trying until a resolve is found.
Where do you live? Others here may already know a local charity that may offer help.
Tony