Why not take the belt off the water pump start the engine and let the engine warm up the water. Then drain off some of the water and add antifreeze.
This is what I was going to suggest. Take the belt off and fire it up.
big thing is she'll be lucky if the block isn't cracked or blown out some freeze plugs in a best case deal.
I've seen some bust the side out.
This is true, but if the damage is done, the damage is done. Starting it up is not going to damage it anymore than it already is. I say there is a good chance the motor is just fine. At worst, a couple freeze plugs might be popped out.
Reason I suggest this...If she ran it without AnitFreeze/Coolant, the water doesn't have the anti evaporation properties. So driving it with water, she probably evaporated some water everytime she drove it, making the water level low enough, there was room for the water to expand as it froze saving the block, and the heads should be fine for sure if it was a bit low on water. One can hope and that's all you can do. Whatever damage is done, is already done so at this point, not a thing to lose by firing it up so long as the belt is off the pump just in case there is some water in the pump. With the belt off, you can also spin the fan by hand to see if it is indeed frozen. If not, put the belt back on and run the bitch and look for water leaks as it thaws.