Why is she treating that kid like that?

I am doing an internship in a kindergarten, we are 4 interns including me. One of the girls acts much more interested, hugging and kissing one of the children in her class. She always sits next to him and looks at him while he eats in the hallway. I wanted to help that child while doing an activity, but she shouted at me. I heard her crying because that child didn't come to school yesterday. I noticed the other day that she took one of his pens. Why might she be doing this?