The mere fact that she's manipulating a phone camera and driving at the same time in four lane traffic is just as dangerous as his tailgating. Had his truck impacted another vehicle and caused injury or death, she could be held criminally culpable, IMO.
Two dumbasses playing tag on a busy highway is what this adds up to.
Considering the video shows her maintaining her speed and lane, and him driving agressively as he passed her, and his attempt to cut her off as he did so, no court should find her guilty of his driving actions. Had she attempted to swerve at him, or actually hit him, prior to his wreck, maybe, but in this case, she's only guilty of being only slightly less of a jerk than him.