h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Yesterday Carrie e-mailed me to tell me she was coming over to give me a painting that she, well, painted obviously. I didn't think anything of it, I told her she's welcome here whenever, as long as she checks ahead of time, just like all my friends. But when I mentioned it to my Father he got rather upset, apparently I promised I'd spend more time with family this summer, and I haven't been, and so he had me call her and tell her she couldn't come, and it wasn't until later I found out she was already nearly here. She got rather upset about it, and she asked me what my father has against her, which of course I didn't know, so I did what any reasonable human being would have done, I asked him what the hell his problem with her is, needless to say that didn't go over well. But apparently he dislikes her because her he thinks her parent's are alcoholics, and he basically has the opinion that she's sort of a whore, and she basically just does whatever the hell she wants and gets away with it, which of course, since I know her very well, I know the last part of that is pretty much absolutely true, but he doesn't know that, he's just acting on opinions he's formed from the few times he's spent any time around her, and I guess just general impressions. He's freakishly over-protective.
So I guess I made a mistake of trying to explain to her what he's got against her, without hurting her feelings. She asked, and she's one of my best friends, we always try and just be absolutely honest with each other, so I thought she had a right to know. I guess it hurt her feelings more than she let on, because I haven't heard from her today, and she normally e-mails me at least once a day, usually more.
I feel horrible about it, because it's not like there's even anything going on between us, she's seeing someone, and even when she wasn't, we've always just been friends, so my Dad's just freaking out about nothing. It's not like I'm a little kid, I'm seventeen, it's way past time for him to just back off a great deal. But what can I do?
Grr...