I think Mac would play with any of these folks! I think she would definitely not get Frank. Mac is not perceptive enough to really understand if people have differences in their brain, but if someone spelled it out she would immediately change her tune. My guess is she'll start off being frustrated by him but come around to realizing she'd been a jerk.
I could see Mac getting close with Andy. Difficult is Mac's middle name and she has a knack for understanding others with a darkness of some kind. She has some major family issues that she really doesn't open up about, and so whether or not she ever talks about them, she is very understanding of others.
Mac might not really get Mary, but put them in a room (a car?) and see what unfolds! Again, she would understand the darkness inside. I don't see a romance here, even though Mac really does like girls, but you never know!
I could definitely see a bff line for Mac and Fabian, though I imagine she is trying extremely hard to keep her sexuality from him, which he may or may not see through, depending. She would love that he starts shit, roll her eyes at his flamboyance and generally enjoy being loud and out there with him!