What happened to Clarisse?

From the text:

"Whole family moved out somewhere. But she's gone for good. I think she's dead."
"We couldn't be talking about the same girl."
"No. The same girl. McClellan. McClellan, Run over by a car. Four days ago. I'm not sure. But I think she's dead. The family moved out anyway. I don't know. But I think she's dead."