female chasing male

[cichlidman3000]

i have 2 female cichlids and one male. the females are a kenyi and a blue cobalt cichlid. my male is a red zebra. today i returned my extremely aggressive male kenyi and got the female. my female kenyi is slightly larger than my male red zebra. SHE chases HIM. i want to know why. i am pretty sure that the kenyi is a female because before i let her in the tank, i did the venting, and also she is blue. i would also want to know how the females choose there males. thanks