obviously xavier knows her. and he apologizes for any time he's been a problem. and sometimes being hard to wrangle. but he likes to think he's one of the easier band members to deal with! whether that is true or not... nina can judge for herself. also he would have kissed her something fierce during the olympics so, enjoy that, nina.
pippa was a slytherin prefect too, and only a year younger than her, so i'm sure they knew each other. friends?
graham was a few years younger and a slytherin, wouldn't have caused a fuss, but probably knows her bc hogsmeade and he's the beer hook up for the band?
otherwise i think that's it? i mean, bill works at the ministry and they might have bumped into each other, but gwenog is older and quidditchy and celia is younger and not really connected with her at all.