Asexuality doesn't mean that you can't have an orgasm! It's only a physical reaction. (A woman can make a guy cum if she is a great cock sucker ... even when he is completely gay ^^ )
Asexuality means you have no or extremely little interest in sex.
And that seems a very suitable description of Monica's behaviour.
I think she told at some point that she had only a few times sex in her life (before the events in the game). It was required to get married to the rich guy who made her life so much better than before. After their wedding it wasn't required for her to do such things anymore ^^
Her "sexual" fetish is being dominant and humiliate insec ehm people around her. She doesn't squirt from it, but it seems to give her similar pleasure