She's saying that spot is perfect, but... if it's on the east side of the house, it's exactly where the sun is going to hit first come morning, since the window is right above her, and the draperies would still let light go in below them, regardless of how light blocking they are, unless they're attached to the wall down below in addition to at the top. (Or, if they're sleeping during the day, then the west side would have the sun hit there first when the sun goes down. Even the north and south sides wouldn't be that safe, actually, they'd be just as, if not more, dangerous for a vampire than if it was the east or west side of the house)