|I do believe in an emergency she would save her Kindle first|
These days even a simple battery has a computer, and being a computer, sometimes it can glitch. Either way, something inside the Kindle has a glitch with charging the battery, and resetting it fixes the problem. I bet they'll do a firmware update at some point which addresses this issue. In the mean time, the missus hasn't had any problems charging her HDX since having to reset it.