I think they're lying about Luna's father.

I think this disease is just as dangerous to purebloods as it is to halfbloods but until someone like Mr Malfoy or Mr Selwyn gets it they're just going to say 'oh, what a shame! he must have been a halfblood after all!' every time someone takes ill. Who wasn't registered as a halfblood already I mean.

Good on your brother for letting her use his owl. I hope her father is alright.