How is it sexism? The person who has two seems to be female.
And from the looks of it she needs a few lessons in grammar and punctuation. She seems new but at the same time not. But from the way that she posts I don't get the feeling that she's going to interact with the other RPers...at least at first or until someone approach her first.
Anyhow maybe Moon Pie (Yes that shall be your name from now on) can explain to this person how you wish to provide more female characters since there is a lack of them and you don't know if or when more people will join. Say that it is for the sake of the RP and you'll do what you can to avoid confusion or to keep it at an minimum.
Although for someone to be unable to tell the difference when some one is playing one character or another I don't have much hope for them as a RPer.