yeah that is a deformity. the guy breeder you bought her from obviously isn't a smart breeder or a good one if he didn't cull a deformed betta. Or maybe he has too many bettas to care for like a puppy farm doesn't care for all the puppies they have so they are brought up in bad conditions. I have many things to say about that breeder but I will stop there. I'd tell the breeder about the problem and also the IBC
America (f, HM), Spirit (m, DBLT), Rescue (f, VT), Missile (m, HM), Purnurple (m, HMPK), Dragon (m, VT), platies, mollies, sorority tank of 21 females, AND lots of guppies.