I want to hit a 4 yr old child that is in in my summer camp class
Why would you want to hit a 4 year old child?
Her laugh makes me uncomfortable.
You should never hit a child especially for something she can't control like her laugh. If it bothers you, you should leave.
I don't like how she laughs in front of my face, but I'm gonna ignore it and do nothing about it.
That is the smart thing to do.   Remember that she is a little kid and that there are many positive things about her that you can focus on.