It could be an injury. It may hurt to move her tail. The pineconing could be from slight swelling underneath. Do you have any sharp décor or nippy fish?
Keep an eye on it & do lots of water changes. If it gets bigger, redder or ulcerated looking consider an antibiotic. I'm thinking you don't have a quarantine tank...
I do have a big bosemani who i've seen go on brief rampages, this morning his whole front half of his body was black and he was chasing all the other fish into hiding except for the female. He almost imediately calmed down and went back to his normal colors after eating.
And i know i should have a bigger tank for bosemanis, but a friend had a male and a female he couldn't keep anymore so i decided to take them since i'm considering upgrading to a 75 gallon soon and getting more rainbows for it.
Also i do have a quarantine tank, but at the moment it has 40 baby guppies in it, also a result from the friend who gave me pregnant guppies with the bosemanis.