I agree about it being female,
The large dark and black area in the anterior dorsal is a female trait. Note the two females below.
and compare the dorsal area of a male below, and the iridescent spangling of the posterior of the dorsal, and body normally on males.
and because the OP raised it alone in a tank, it is the dominant one, the alpha, which would account for the nuchal display not seen on non-alpha females. This is common in many cichlid females that have alpha status, and no male present.
Below a dominant female haitiensus as an example.