This sounds like the power is completely depleated. This exact same thing used to happen to my husbands 3GS. The problem was that it was depleated of power. The battery is dying and cannot hold a full charge any longer or is faulty.
Try plugging it in and let it do it's thing. You may hear it cut on and off a few times but you will see the red bar in the battery when it finally comes back and it will come back when there is enough charge. You will also see the Apple logo. Don't panic, the phone will come back.
A hard reset will not help this. The battery is dead and or it's faulty. Just plug it in and wait a bit until its charged and then let it charge fully. Your daughter should monitor her battery because it sounds like it's dyring. So this doesn't happen again, she needs to get juice to the phone when it's probably at 50%.
This is just the symptom of a dying battery that can not hold enough charge any longer, or a faulty battery that needs to be replaced.