If this is a mature fish, You have a girl on your hands.
The caudal end (ass end) of the dorsal (back) fin, when raised, will NOT pass the peduncle (the border between the muscular body and tail fin) ... females tend to line up straight- the boys are a bit more flamboyant.
She looks big enough to tell for sure. The dorsal fin will always originate along their back- the key is how far does it extend toward the tail.