IMO adding a large pleco is actually asking for trouble, which is why I asked. The fact that a FH accepts a pleco doesn't equate to it accepting another cichlid, female, or not. That's what tank dividers were created for. It allows the prospective couple to get used to each other for a period of time, before you let them mingle. Even then, bad things can still happen, and sometimes very quickly.
Large plecos have large spines in their dorsal fins, and I've seen more than one FH (as well as other large aggressive CA's) get seriously injured when attacking a large pleco. The last time I saw this close up & personal it involved an adult male RT (that I previously owned), that ended up dieing when the wound (in this case in his mouth) became badly infected.
But hey, it's your fish.