thank you V. I really hope it doesnt get any bigger. She swims fine and eats like a pig and even still plays with the other fish. just as she always has since we got her.I think neon tetra disease is unlikely if you've had the fish more than a month or two. It does looks like it might be a tumor to me. If it continues to grow then it will may kill the fish. If it doesn't grow you'll just have a shub with a bump.
Other than the bump the fish looks healthy.