The girl is
traveling southbound on 121 near Grapevine (with reportedly twice the legal limit of alcohol in her system) and hits a highway divider causing her vehicle to end up in the inside northbound lane. Moments later, a northbound motorcycle strikes the wreckage killing the rider.
The Intoxication Manslaughter statute is applicable if the person "is intoxicated and by reason of that intoxication causes the death of another by accident or mistake." "Causes" is not defined.
There is no way the DA's office in Tarrant County recommended a "no bill" (a refusal to indict) since they love to jump all over these kind of cases. I'm guessing the grand jury, in a moment of rebellion, decided to ignore the DA.