She isn't being tried for murder. There is a distinction in American law between murder and manslaughter. I believe she is being charged for an even more indirect crime "Involuntary Manslaughter."

MGL Chapter 265, Section 13

1. An unlawful killing that was unintentionally caused as the result of the defendants' wanton or reckless conduct;

She waived her right to a jury trial and so only a judge will decide if the young man died because of her reckless behavior.