I'd diagnose a bad battery (the amazing thing is that a battery that's been that badly treated [bringing it down to 0% or 1%] has lasted 7 years).
Tell him to have the battery replaced, and start getting in the havit of charging it when it drops to 40% - he won't be as lucky with the next battery.
Time for a new battery, but I'd also consider replacing the tablet itself. I'm sure it's suffering from other performance issues as well due to its age, and it is no longer getting security updates.
She did get the battery checked, "fixed" it but it still shows the issue. I know it's pretty old, but she can't get a new device
What did she mean that the battery was "fixed"? It sounds like it has to be replaced, but even then, there could still be a problem, since any replacement battery for such an old device has also been sitting around on a shelf for a long time, and could therefore also be halfway (or mostly) dead.
Agreed. Batteries deteriorate over time, even if just sitting on a warehouse shelf. It's pretty much certain that no one is still making batteries for this tablet, any "new" battery out there is likely done for already.Just to make sure it's not due to some 3rd party app, see if the problem happens in Safe Mode as well: https://support.t-mobile.com/docs/DOC-28805
Otherwise, the only thing I could suggest is to keep trying new batteries until you find one that isn't completely deteriorated -- but by that time, she would've spent more money on trying to fix this tablet than it would cost to get a decent replacement tablet!