I had something similar with Amy, when she was the same age. only hers was on her side. The result of the biopsy came back inconclusive. Had it come back as cancer I "might" have gone for an op, but her health was not good in other ways so as they could not definitely say cancer I said no to an op. I'm personally sure it is cancer, it is continually weeping, but it does not worry her, even now at 14.5 years old. So I'm sure I did the right thing. Had she been still fit when it was first found I might have gone with an op. But quite frankly it's something only you can decide. Operations are never without risk, and the risk grows with age. The biopsy is not a problem. If she is steady they can do that with nothing. if she is very apprehensive then they may need a sedative, but I'd think nothing more. Then at least you will know what you are looking at. If it turned out to be an aggressive cancer then my attitude would likely be, "Well I have nothing to loose, so go with an op on the grounds that it might buy me a little more time with her." If not so aggressive then possibly leave well alone as the risk is greater than the cancer.
So sorry, not much advice from me. Whichever way you jump you will be doing the right thing as you see it. And that, sadly is the very best anyone can do.
Thinking of you, John