"She was using an off brand charger"
There's your issue right there.
She has damaged the U2 IC chip, the message asking you to use a genuine charger (even if you are) is one symptom of it, more severe symptoms are:
- Overheating
- Fast battery drain (even in airplane mode)
- Phone charges when on, but if left to die, will not charge, but is able to come back on with a charged battery
The only fix for this is to replace the U2 IC chip.