Rachel was indeed a cartoonish secondary villain at first, but imho the concept of her character changed with the plot’s progression. She clearly has some personal issues that have yet to be understood. In this regard the development of her character is somewhat similar to Catherine's. So far, the main message of the game is that everyone (well, okay, almost everyone) deserves a second chance and can find a place where they are welcome (at the cafe, obviously). And so far, it seems Rachel is going to get her second chance, too.
I'm not sure she will be “redeemed”, or that her “new” character will be interesting (and not cartoonish), but I’m sure her story hasn't really started yet.