I have quite a few characters for you to pick from.
Isadora Kirke - She's a Hufflepuff fifth year like Kate and she's generally quite shy and retiring, doesn't have many friends. She'd be quite happy to be Kate's friend, though! I doubt they'd be particularly close but perhaps they study together or something? Dora is a good listener too so Kate could rant at her all she likes.
Cerelia Avery - A Ravenclaw sixth year, she's quick-witted and very acerbic. She's not very kind to those she doesn't trust and often has a nice, thinly-veiled insult waiting for anyone that talks to her. She has serious propriety issues and is trying to find a foothold in Pureblood society as a woman and while she isn't overly fond of Hufflepuffs, she does have a knack for Potions and could be a help to Kate in that department.
Melissa Finnigan - She's a free-loving, sixth year Gryffindor who smokes too much, drinks too much and ran away with her on-again-off-again boyfriend to the caribbean so she's no use to Kate currently.
Elliot Finnigan - He is Millie's twin brother who does much of the same but isn't as fun and is much more broody and miserable. He's got no time for idiots and was once a fierce rival in academia to many of the Ravenclaws but he's lost the will to go on and would rather layabout. He could probably be maybe an attempted flame on Kate's part? Sort of, they tried to date a few times but never got into the swing of it and gave up and are probably friends..
Cordella Quinn - My Slytherin! Sixth year, again. She's a bit of a bohemian, just like Millie but has a little more restraint, less tattoos and is rather fond of girls; which might benefit Kate's inner turmoil - or it might not. Della's scene is mostly seedy clubs in Dublin or Belfast and she bobs around her home country of Ireland a lot. She has a habit of disappearing and is currently dating Gisele Delacour - not that anyone knows - but I reckon she'd be a good friend to Kate; she doesn't have a problem with anyone.
Daedalus D'Eath - My other Slytherin! Sixth Year. He's dying. He's perpetually in a mood because of that and is no help to anyone or himself. He's no fun. XD
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