In the Kindergaden, our 2.5-year-old daughter has periodic confrontations with a 5-year-old boy, who used to hit her on the head with a toy. She is totally scared of him up to not willing to go to the Kindergarden.
What are modalities before changing Kindergarden - try to explain something to her she should e.g. shout aloud for help, or talk to parents? How not to let her alone with this? How much is to protect and how much to learn to react properly? In general she is full of courage, so not a fearful kid.