Make sure to sing the Un-Birthday song to everyone except her! Maybe throw her a tea party, and ask that all guests dress up in their Sunday best? See if you can find a blue dress for your sister to change into after the initial surprise. You could play cards at a picnic table, and set up a croquet game in the yard! Maybe paint the mallets pink and decorate them to look like flamingos, and decorate the ball to look like a hedgehog, and glue cards to the wickets? You can look up how to play online. Be sure to sing the Twinkle Twinkle Little Bat song, and possibly have someone recite (or sing) The Jabberwock, this really cool poem that Louis Carroll wrote in 'Through the Looking Glass and What Alice Found'. If you can, maybe get her a kitten named Dinah for her birthday? have everyone talk in an English accent, and maybe make a cake shaped like the Cheshire Cat, or a pocket watch? Serve drinks in little bottles (available at craft stores) and tie a piece of parchment paper around the neck that reads Drink Me. Tie another one around all the food items that reads Eat Me. Make a rabbit hole as the entrance to your party- tape a cardboard box to the back door and put a curtain all around it so that to get outside to the party your guests have to crawl through the rabbit hole. Maybe you can stage it so that it;s the last thing you put up, and when your sister finds it she'll be just like Alice crawling through the hole. Maybe leave a Drink Me bottle just outside so she knows what to do! And you could play the 'Painting the Roses Red' game, where you print off pictures of white roses and everyone sits in a circle. Only one picture goes around at a time, and the players colour the rose with red markers, passing it off to the next player as they wish. When the 'Queen of Hearts' jumps out and yells OFF WITH YOUR HEAD! then whoever's holding the rose is out.
Hope this helps, because this sounds like a fantastic party! Can I come?
Another Alice freak!