Lets just say if she values walking she should stop doing it.
Or if you value her life in the slightest, you would stop her.
If anything happens it will be on YOUR hands.
If you are unwilling to keep her safe, I am willing to contact CPS for you.
But is there a study based in real life? I would think that the worst is that she would get a broken nose/facial fracture from her knees hitting her face.
Use some common sense.
If you do not care about her, then by all means let her continue to risk her life while in the vehicle. But if you care in the SLIGHTEST, you would stop her.
might as well post this
Patient was a front seat passenger in a car and had right foot on the portion of the dash where the airbag deploys. The car was involved in a low speed (25mph) crash. The passenger airbag deployed, tearing the foot from the tibia and grossly dislocating the talus. Driver was uninjured.