I just had a vision.. Maybe Tai was always a girl and they have been dating(would make sense, considering their attraction to art), and she wanted to be a Mod and was like "no sex until you mod me".

Chruser was worried there would be some sort of upset about him making her a mod right off the bat, just because they're dating, so he helped her draw some pictures and then that gave us an excuse. Well, even chruser knew that nobody would believe a chick could draw such sweet ass pictures, so he changed the "Gender" thing to male, when she wasn't looking.