[jedifarfy]

Hold the top button down until it turns off (15-20 seconds). There are other instructions. Let me go find them, I can't remember them all off the top of my head.

Edit: Ask her if she had it charged. This seems to happen most often when people ignore the charging warning and keep reading. Remove the battery, replace it, hold down the button. If that doesn't work, take out the battery and plug in the nook to the power. The nook should come back to life and unfreeze. Turn it off, replace the battery, and try charging again. If the battery won't come back to life, she's fried it and you'll need a new one.