My suggestion for the south dorms is a a bald Minkan male named Lobsang, who smiles a lot and has a wicked streak a mile wide, despite putting on the appearance of a pacifistic ascetic.
My suggestion for Sarena's opponent in the fight is a tiny Neko. I mean, one that's under five feet tall. Not a mini-neko, Sarena would lose by doing the cartoon elephant-reacting-to-a-mouse thing and fainting. Name Maki Takara, green eyes, long black hair in a braid, very bold and energetic.
I'm thinking Sarena will lose for most of the fight, until Takara gets incautious about her stance and guard.