I could see her doing something like that, but I also kinda think she has just fallen for his dick. Much like how each player can interpret for themselves whether the MC is dumb as a rock or is secretly into it, etc., I think there's room to interpret what Liz thinks of the men in her life. My opinion is that she still legitimately likes having MC as the "romantic boyfriend," but in keeping with the NTR porn logic of games like this, she has developed an insatiable lust for sex with Matt. It would be hard to imagine a situation where Liz went over to Matt's house wanting to just watch a movie and cuddle (regardless of how Matt would respond). She only goes over there to get fucked.
But you know, everyone is free to read between the story's lines however they like.