Ava & Abby
Abby will be a 3rd year Puff, so I can see them being friendly, even if not great friends due to the age difference.
Ava & Amber
Amber, 7th year Slyth, would probably be one of those purebloods that Ava would hate. Amber isn't all about pureblood supremacy, but with the pro-muggle leanings of the world, she appears to be more than not.
Ava & Blythe
Blythe will be a 4th year Gryff. She's a spoiled little princess and this doesn't exactly win her any friends. We can toss them together to see how they react though.
Ava & Caryn
Caryn is a Gryff in Ava's year. Not sure how things would go with them, especially since Caryn is friends with Keira due to the 'pureblood-like' Yule parties Caryn's parents throw. Could be interesting though.
Ava & Emily
These are the two I can see being good friends from Ava's description. Emily is DEFINITELY non-confrontational. She kind of ignores conflict as a whole. It doesn't fit into her sunny view of the world. (Emily doesn't even notice one of her year mates bullying her, for example.)
Ava & Sasha
Sasha is a Slyth a year below Ava. I don't think they'd end up enemies, but I'm not sure how well they'd get along, simply because I'm not sure exactly how much interaction they'd really get.
Ava & Alannah
Alannah is a server at the Leaky Cauldron, so that would be the most interaction they'd get, I think.
Ava & Cassie
Cassie may or may not help out the school nurse sometimes. Beyond that, unless Ava goes to St. Mungo's, I don't see much.
Ava & Jacinth
Jacinth is a Hit Witch, so unless Jacinth does something at the Summer camp, I see nothing here.
Ava & Kyna
They'd definitely have interaction if Ava takes Divination. Kyna is the professor.
Ava & Portia
Considering Portia is an assassin, let's hope there's nothing. LOL