Isabelle - > Is in Ebonhide and also in Choir, so they have some overlap there. Issy is likely one of the few people who has no idea about her mom, because she didn't start Gooseberry until the beginning of this current school year, so she missed all that. In turn, your character knows nothing about Isabelle's very public meltdown at Ilvermorny two years ago, so they can be those superficial friends who know zero about each other's deep dark personal secrets. Issy likes overbearing personalities because they make up for her own shy, nervous one. ALSO Nia never has to worry about Issy breakign rules because she's SO BORING.
Avery - > JR, some overlapping classes, but not much in common. Avery does love people though and is pretty nice, and would never bring up the mom thing or try and discuss ~feelings.~ Avery guards her own secrets and feelings pretty closely too, but she's always got that smile & happy going on and she likes to follow the rules too, a lot. Though she's broken a ~few~ more recently to stop being such a nerd.
Penelope - > HATES ALL THE RULES, BREAKS ALL THE RULES, IS AN AWFUL HORRID PERSON. She's emotional and rash and says all the wrong things and I'm not sure they would get along real well unless Nia took the time to break into Penny's softer inner shell.