Okay, so if she's an order supporter, she's probably acquainted with Gideon despite him being a few years older. Since she's a Quidditch player with that bunch, perhaps she joins in their occasional pickup games? If she does, she might know Ted Tonks as well, since he frequently joins in.
Sarah Cornfoot, alas, is too much older for her to be likely to know her. However! The journals are full of interaction opportunities, and Sarah is v. chatty. :)