What the heck is this? Injury?

[Treg]

Did she get cut by another fish? I don't know if I have ever seen anything like this...

No new fish (disease's) have been added to the system in almost two years.
They were moved into a newly setup tank 10 days ago, though.

 

[DrPat]

looks like trama induced and chasing or fighting going on

 

[VeL]

Similar injury on my clown i've seen once and it was from an yellow tang's bite while in QT. Funny thing then is that I thought the fish is a goner cause the wound was on its belly, the blood has coagulated and looked like a gut coming out from him.