We need more seventh years, definitely! Still, Ruby being a prefect means she'll still have more than enough reason to interact with people.
Anyway, let's talk about mine...
Cormac tends to be a little disrespectful to prefects, though thankfully not in a "hey, please put me in detention" kind of way - and the fact Ruby is a Gryffindor prefect might help things a little. On the other hand she's Mel's sister, and Cormac and Mel have that interesting relationship going on, so I guess we'll have to wait and see how things go in game.
Hamish and Samir will be friendly but, again, we'll have to see how it all goes in game in terms of interaction. OOCly, Samir would like Ruby to know that things are very nice outside the closet, and the air is a lot fresher. Plus there's coconut pie.