She probably put the shotgun under her chin and flinched when she pulled the trigger. If you do it correctly (in the mouth pointed towards the back of the skull) you would not survive.
I wouldn't say this is 100%, but probably greater than 99%. Her other mistake was doing it at home with people around. Had she put the barrel in her mouth, a 20 or 12 gauge would either have killer her instantly, or she would have died from the trauma to other tissue or bleeding very shortly thereafter.
I have said numerous times on these forums, if you are going to use a firearm, only use a shotgun, rifle caliber 308/7.62 or bigger, or 44 or 45 handgun. And only in the mouth. Will smaller calibers or other placements work - maybe. But there is that chance you wind up like this girl, fucked for life and on constant suicide watch. Also, she will never legally be allowed to purchase or own a gun again.