MandM,
I have an adopted gifted daughter, too (adopted from Russia and is now 8)!
This may be a long-term issue. I myself remember DELIBERATELY answering questions wrong on a test on which I ended being the top scorer.
We are wise to let our kids know about being gifted right away, and how they may be tempted to "hide" their brightness. Your daughter is so young, I wouldn't worry too much about it now. She may grow out of this shyness. On the other hand, as she progresses in school, she definitely needs to be told how wonderful it is to be gifted, how many people may benefit from her gifts etc.