Posting a pic would help. I had a female angel with the same problem a while back;

I made a few calls to national fish pharmacy, and talked to some angel breeders. Spawns from this female paid for most of the gear in my fishroom, and she was the female out of my first pair. I treated with metronidazole at first, then paracide-d. Clout with epsom salt finally did the trick, took about a month for the swelling to go down.
She is in a 55 with a group of other adult angels now, the male has since been re-paired with another fish. She has shown no signs of spawning, she quit spawning around 8 weeks before the tumor appeared.