She's not hungry she's stalling...my son used to do that all the time! Most kids are "grazer's" at that age and will eat smaller meals throughout the day. It never failed at bedtime he would say "Mommy I'm starving!" and I would give him something like what you are giving your daughter, yogurt, some cheese, a little fruit, etc, but it didn't take me long to realize he was just avoiding going to bed.
My advice, let her have a small snack, like you are currently doing, and then NO MORE! Add to the fact that she is just trying to avoid sleep, eating anything makes the prefrontal cortex of the brain more active. You are giving her brain fuel late at night (especially with the carbs because they are higher in glucose which is THE fuel your brain uses to run)which can make it more difficult to fall asleep.
Here also is a great article for you on how a child's brain will react to foods of all sorts, and some neat ideas on grazing trays that could help you out late in the day! (first part is a few recipes, scroll down for the full article)
http://www.askdrsears.com/html/4/T040400.asp