Most folks who misfuel and drive until it dies will be ok with a drain/new fuel filter/flush/refill with diesel. But it should be noted that it is possible to damage the injection pump, injectors, and even the pistons/block under the right circumstances, and damage to those parts may not show up for a while. That your sister repeatedly restarted and drove until she got it home increases the likelyhood of extensive damage. She should not have done that, she should have given up the attempt, parked it, and called for help. Under the circumstances, I doubt the fuel vendor can be held liable completely.
Here's the deal, for any newbies who are reading this. However it happens, if you wind up with a significant amount of gasoline in your tank, STOP right where you are to minimize the damage. If you realize it before you start it up, all it takes is to drain the tank and refill with the right stuff. If you start it up, you've added a new fuel filter and fuel system flush to the cost. If you drive it until it dies of its own, you might need a new IP and injectors, or more, and now we are getting into some real money.