The kids (my niece and nephew) I interact with at that age are pretty willing to do just about anything so long as there's adult interaction. (They're also really good at entertaining themselves by reading and playing alone, but when I see them, I get to focus on them for a bit.) Adult interaction may also be especially important if she's worried about her sister or if she's been feeling left out (if the parents have been focusing on the other child).

I really like that craft ideas and holiday ideas that people have come up with.

I have had a great time doing gingerbread houses (you can make the houses out of cardboard, and either buy a couple tubs of cheap frosting or make it yourself. Food coloring and some random candy, and voila. Hours of fun, AND it's a cool thing to get to display for a little while.

We've also done tie dye, painted birdhouses, played endlessly in the park (kids don't tire quickly of swings, at least that's my experience).

Board games and legos are also big for us.

Finally, my niece especially likes to help me with cooking stuff. Bake some cookies together or something, make pancakes, whatever.

And a visit to the local library for books for down time