I dunno, I think I would try another approach. I would tell her that I don't really do that whole gift giving stuff, but when I see something that I think a person will like, I get it for them. That way it will show you care about what you get her, but then she doesn't have the guilt associated with feeling like she's going to get an expensive gift every holiday.
However, this reflects more of my personality. I think telling her it was markdown is another solid plan as well.
Gluck sir and welcome to SF.