If its definitely a lymphoma I would say surgery isn't an option. It is something that is likely to have spread. I've just been reading about lymphomas in hamsters. But I'm just wondering if the vet diagnosed that as a possibility or an actual diagnosis from tests. I mention that because Moo's large lump on his chest was diagnosed as a mammary tumour (some info about those in the link below which includes a photo of a very large one on a rat).
To me, I would want to know if it was definitely a lymphoma or not before deciding whether surgery is an option, but from what I've read, the only way to tell that is to do a biopsy.
Mammary Tumors in Small Mammals | LafeberVet
From what I've read of lymphomas they're not usually just a lump but other health issues and skin problems as well. Do you have a photo of her and the lump?