Millie Potts is a fellow Ravenclaw, and this year they're finally in OWL classes together. I get the sense that Millie and Bonnie are either turned off by the other's social extremes, or they manage to fill what the other lacks somehow. Millie, from what I read in their bio, seems like all the things that Bonnie might not want to be, the struggling student trying to be a good role model, learning to be a proper lady, and willingly living up to others' expectations. Could make for interesting dynamics for a social or classroom encounter, Millie excels at Charms and Transfiguration if Bonnie needs tutoring.

Now, for Charley, she will happily enable any girl (it probably doesn't make sense to her that Blair doesn't see themself as one) who prefers the dress and behavior of a boy. If Blair gets out for Hogsmeade days, Charley would happily introduce them to the fun stuff around town, get their nails dirty, and teach them how to dodge the chaperones more easily. I could see them being easy friends if you're interested, they seem very compatible with Charley.