I have to say it was probably at least on other factor other than speed.
I think not being focused on her path of travel may have also been an issue.
I'd say speed is what did all of the damage and took her life.
But a vehicle the size of this semi she hit, should have been large enough of an object to have been seen a good way back if she was watching where she was going.
Of course all of the details to this crash may never be known with the driver taking the real cause of why this happened to her grave.
A lesson to all drivers you are better off obeying the posted speed limit,but above all else be rested and keep your mind on what your doing at all times.