If you are going to still be there late into the reception, I would ask her then. Every wedding I have been to, things have been much more relaxed and social after the 1st dance, and cake cutting, so I assume most are like that?

If you think there aren't going to be a lot of gifts, then I don't think it is inappropriate.. I wouldn't ask if there are lots of gifts and others then might feel left out and want theirs opened too..