Charge it with the power off for 24 hours straight. See what happens after that.

10% isn't enough to really power it on - it comes on long enough to show you that it has no power, then shuts off. (Discharge a Lithium Ion battery too far and charging it is dangerous, so internal circuitry in the battery will disconnect it from the contacts, and you can find a safe disposal place for it. Resetting it will cost more than a replacement battery.)

The charger isn't an external power supply - it's a charger. You can't supply enough current through a USB 2.0 connector to power the device, let alone power it and charge the battery at the same time. If she has to have it running 24/7, she needs a second battery and an "out of phone" charger. (There are some good ones sold on Amazon.)

 

I would say the USB controller is toast in the device and a new device is in her future.

As for not being able to run off a wall charger, some low power devices can, but then you may as well just use a corded phone. As for powering + charging, unless you're using a junky charger, this is false under normal use (I have outpaced a computer USB charge under normal use on other devices).