You
SHOULDN'T be breeding her, that is for certain!
A: You need to put her in
QUARENTINE. You do not know what the tumor is, and if it is contagious and spreads, you will be giving your fish death sentences. You may be young, but I don't think you want to do that, do you?
Then, you need to get a camera, and take some pictures of the growth, and post them to the forum... or get out your most descriptive abilities and tell us what it looks like, etc.
Frankly, you should ditch the idea of breeding. If you can't identify and tend to diseases in your fish, how do you think you'll keep baby fry alive? The instant they get sick, you need to be able to ACT, not spend three or four vital hours asking questions -- by then it may be too late.
Seperate all of your fish into SEPERATE containers. Look at them for symptoms. Treat them for the various illnesses that they have brought in. Don't put them together for at least two weeks until you KNOW they are no longer sick. The males stay -away- from the females and in their own houses, and you should only keep the females together if you have a PROPERLY set up aquarium. This means at least ten to fifteen gallons with HEAVY plantings of java moss, and other types of plants, caves, etc for the girls to hide in. Then you need to babysit that tank until you know for a certain that the -minimum of four females- gets along well.
Maybe you haven't already made a very drastic mistake...
and dont breed veiltails 
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