First, was she using the stock Motorola power adapter or not? If not, then quite possibly that charger has failed. Althogh dlallen66 has raised a very good point. Still, using other than the power adapter supplied with the phone (or an "approved" adapter - either Motorola's or Verizon's), is not recommended.
Although all MicroUSB connectors will fit any phone which has that port, and even though the standard for MicroUSB Charging dictates that the voltage is 5.0 V, +/- 5% (4.75V - 5.25V), the quality of the power can vary widely from high quality charging adapters manufactured by name brand manufacturers, to cheap generic adapters manufactured by low quality mass production manufacturers - most specifically those in China which are build very cheaply and with very little in the way of power regulation and filtering.
The use of non-approved wall or car adapters can result in power which can fluctuate beyond the specified voltage limits, and power which can be full of ripple, noise, and RF Interference. This "dirty" power can stress the components of the phone's charging circuitry, as well as add stress to the battery. Depending on how badly the power is regulated or how much interference in included in the power, the power can actually damage the phone or battery and such damage can be permanent.
It is mentioned in the user's guide for the phone that if you use a charging adapter other than an "approved" adapter, you may damage the phone and void the warranty. Overheating of the battery will damage it and although the battery may "seem" to be OK if you revert to the stock charging adapter, there may have already been considerable damage done to the battery which can shorten its lifespan considerably.
There are plenty of others out there in the forums who will disagree with my opinion regarding the use of charging adapters manufactured by other than the manufacturer of the phone, mainly because they've used a wide variety and have never experienced problems with them, however why risk it? Duplicate power adapters can be purchased quite cheaply and by staying with the OEM charger adapters you assure yourself that the phone will be receiving the proper voltage and current as recommended...and that it's clean power under all circumstances.
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