I'm Bee and I play Mandy Brocklehurst, Theo Nott and Gwen Montgomery. I think Mandy should know Luna fairly well. They'd have the few years at Hogwarts as well as the last few years in the Underground. I've always had Mandy think that Luna's excentric but in the smart sort of way. They're probably not close friends, because Mandy was never good at making friends so generally stuck to those in her year, but she'd never behave negatively toward her.
Theodore would likely not bother with her, and Gwen was likely the sort to have picked on her in school with her friends. So yeah... but welcome! and if you want to plot or anything, my AIM is Mandy Nott Lilly