If the weather is still nice enough, have a small outdoor picnic. Mostly with just lots of balloons (kids LOVE them). For my daughter, I got her a new doll with feeding set (bottle, spoon, sippy cup) and some boots (she loves shoes :P)
Get balloons today and when she wakes up, have her room filled with balloons! Let her pick whatever she wants to eat. Sing to her with candles for every meal. Just get her a doll or something simple. Make the day special by doing something great - go to the park, or zoo, or even the pet store. You could do her nails.
Of course you can have it on saturday!! but have her a little cupcake for lunch and shes a girl honey, take her shopping and let her pick out something! :) that way you know she will like it and you get to have a girls birthday shopping day!