Advice?

Ha

So there’s this girl… I wouldn’t exactly call her a friend but I wouldn’t exactly say I’m not on friend like terms with her, she’s pretty toxic and I have been thinking for a while that maybe I should cut her off, I finish school in a couple of months and I think I should wait until then to cut her off, but my best friend and boyfriend want to do it sooner, and technically they have. This girl definitely knows my best friend doesn’t like her, and I think she’s unsure about my boyfriend because he’s nice to her cause he is in a couple of her classes… she lives near me and I have to catch the bus home with her everyday, and I don’t want any drama which I feel might happen if I told her I don’t like her as we have a mutual friend. I have no idea what to do… my boyfriend and best friend want to reiterate to her (as the three of us) that they don’t like her, but I feel like my situationship with her is different to theirs and confronting her as a group like that may be more trouble than it is worth as she has unstable mental health issues and uses that as an advantage to get what she wants sometimes (I know that sounds toxic of me to say but trust me she’s using her mental health as an excuse in a way she probably shouldn’t.) What do y’all think I should do?