So this isn't legos (but if your DD is meh on legos, I probably wouldn't really push them--just choose something you know she likes), but how about an Easter/Spring tea party for the family party? Your DD sounds like she leans toward the girly stuff, and this could be easy and fun to pull off. Set a pretty table with fresh spring flowers, serve tea in fancy cups, have plates of mini cucumber and chicken salad sandwiches, fruit salad, and some decorated cookies or petit fours in spring colors or shapes. If family like grandmothers and aunts are going to be there, I'd think they'd love it :-)
If by "family" you mean lots of little cousins, then this may or may not work for you. If you've got younger cousins to entertain, you could do a bunny themed party (serve cupcakes with Peeps on top, do the bunny hop, play hopscotch, give bunny ears for favors, etc.).
Mom to J 6/25/08 and M 6/21/11