New bump on my Dumpy?

[elly]

It might be an abrasion from something in the tank. That's a best case thing and it kind of looks like a scrape or cut. Some parasitic worms leave bumps and maybe either they're not all out yet or they didn't die.
I'd keep a close eye on her, check out her skin and belly for signs of redness and bleeding, take her to the vet again if she stops eating or there are additional marks.

It looks like a cut, honestly.