P.W.
Talk to her teacher. Sometimes children will tell you something that may be a true experience for them, but it may have been for one day, or even one hour. They move on and forget about it while we are stuck in worry land.
I'd say give it time and if necessary check out the teachers perspective. It may just be beginning of the year finding her niche. In the meantime have her invite some new friends from 1st grade over to play. They may just do the trick.