I think you are probably right that it may be a tumor.We took her inside the other day and gave her a nice wash. A lot of the old blood washed off but then some of it bled as if it wasn’t old blood. We believe she has a tumour, and are just keeping an eye on her as is still bleeding sometimes
I'm thinking your girl may have something like this
https://www.backyardchickens.com/threads/infected-leg-wound.1280675/