I hated this growing up. My mom would asked me to do things, and I'd do them when I felt like it, as she never communicated that she wanted it done right then and there. we had many a fight over that.
As I got older, college, and after when I was still at home, we had epic battles over the holidays. We would have company, and my mom would ask me to help. fine. I'd ask "what would you like me to do? she'd say "please vacuum the LR and DR" I would do it, then say, "ok, what next?" she'd say "give me a minute" which turned into many. I'd get tired of waiting, and go read or watch tv, and she'd come by, sigh and say "'must be nice to be able to read/watch tv"
I finally broke her of this habit by telling her I was happy to help her out, but only if she gave me a list of all chores she wanted done. this way I could do one, move on, and so on. And if no list was provided, no help would be given. it sounds harsh, and makes me sound bratty, but we both realized it worked.
EVen today when I go visit her, there are always some things she needs help with, so we do the same thing, and I will ask, what needs to be done now, and what can be done before I leave (I usually stay a week or so).
I like the suggestion someone made about if she packs now, you will help, but if she waits, she's on her own.