A matching dress for her and a favorite doll is fun at four, but my favorite project for that age group is "crayon aprons".
I make a lined short apron, turn up the lower edge about three inches, and stitch lines from the upper edge of the "pocket" across the entire folded area just large enough to put one crayon in each little slot. If you buy the box of crayons first, you will know what size and how many crayons slots you will need. These are wonderful for car trips, visiting 'boring places to a four year old' to keep them occupied. Pick up a couple age appropriate coloring books to carry in a matching tote, and little ones are ready for whatever comes to keep them occupied. You can embellish as desired.