Suggestion needed!!

I have 5 yr old girl. She s a happy kid. Have had very gud & troublesome times with her.

Last nite we had been to gettogether.. One of my friend has a boy. He hit very lightly once long time back.. Every time they meet my daughter is so scarred of him that she starts crying. She was crying for the next 2 hrs.

How do i make her to get over this fear? What can i do if something like this happens in school??? How can i protect her there?