What body protector was she wearing? I've landed flat on my back a few times in mine, Normaly at high speed.
Mind you my body protector cost over £100 and was made to measure
This is the one I have: Rodney Powell- The Elite – Powell’s Best Selling Body Protector
They are only about an inch thick and they are foam so they shouldnt be able to do any damage. If yout shoulders wont flex 1 inch then you have a very serious medical problem