[B/s] Film recommendations with positive incestuous relationships in the plot?

My sister will be coming over next weekend. We'll be alone at my house and drinking. I don't know how my sister actually feels about the prospect of having sex with me but I suspect she has similar desires. I think we're each presenting a degree of socially mandated propriety on the subject because if one let the other know directly and it was received poorly, it could harm our relationship. I've been very slow and subtle. I have picked up on hints that she's playing the same game back--but of course, hints that can be easily played off and nothing definitive.

Suddenly, it hit me: she's coming over and we're going to watch something on the TV while drinking and having a good time, so why not pick a film that can bring incest to mind and help things along? Unfortunately, the only thing I've ever seen which touched the subject in such a way is the anime "Koi Kaze." That won't work because it's too long and has some mean negative parts that could shut the whole idea of incestuous relationships down cold. I'm coming up empty on other ideas.

Anyone here happen to be a movie buff with a good incest film recommendation for this rendezvous? Edit: can't be a horror film or a psychological thriller, from experience I know she doesn't like those and they make her uncomfortable.

Update: Seems things have either changed or weren't as far along as perceived; nothing risqué came of it, just a good friendly tipsy time, so...move along, nothing to see, but THANKS for all the excellent movie recommendations! I didn't know most of these existed and I'm looking forward to seeing them.