A black screen when dropped is an 80% chance the screen will need replacing. However do try the above method first mentioned by Xgm541, that should restart the phone. If no joy then you will need a new screen i'm afraid.
That's the first thing i did. I pressed both buttons until the backlight was off. When i restarted it afterwards, the screen remained black and the backlight was back on
That's the first thing i did. I pressed both buttons until the backlight was off. When i restarted it afterwards, the screen remained black and the backlight was back on
The phone has a broken LCD the backlight cable is soldered to the LCD cable so it's not a loose cable. It's almost as expensive to replace the screen as it is buying a new one. I would recommend just upgrading her to a newer phone it's not worth staying at that model.
There's a chance you might've popped out the ribbon cable for the display. Hop on over to iFixit if you think you can handle it or give it to a techie friend. Worst case scenario, the shock irreparably damaged the LCD and you'll need to buy a new display/digitizer assembly. I'm sure they run pretty cheap for the 4S now.