Could she have bought vodka on Sunday?

Did Diane pass through any states that sold liquor on that Sunday? I'm trying to determine which of her actions were premeditated and how long in advance she decided to do them. For instance; did she already know she was going to drink and drive when she left the campground, and that's why she threw the bottle of vodka that was supposedly kept in the camper into the minivan? Or, did she, for some reason, stop on the way home and buy it? I take what her husband said about the camper bottle of vodka with a grain of salt. It seems just as likely that he made up that whole story. We know she didn't buy liquor from the gas station that was shown on the video, but maybe she stopped other places that nobody knows about.