How to support students with selective mutism

So recently I got my first ever real job after graduated from college, I became a shadow teacher at an elementary school. There, I met a student who I suspect might have selective mutism. She doesn't want to talk to anyone, and she doesn't seem to want to listen to anyone either. She interacts with other students, but still without talking. Her parents said that she talks normally at home. A few days ago, she finally spoke to me. She just said, "Dizzy," so I let her go get some water at the back of the classroom. But then she stayed there until the end of the class, playing with the wall decorations, and refused to go back to her chair. It turns out she does this a lot to escape the classroom. Does anyone have any tips on how to deal with her so that she can actually learn something from school?