You could try running in Safe Mode and see if it stays on. Safe Mode is a diagnostic tool and Play Store apps don't run, helps to determine if apps are causing issues. No data is lost or deleted. It kind of sounds like a classic battery failure.
Well it's acting temperamental now. It will stay on for some time and then all of a sudden it will just shut off. I guess she's getting a new phone. I was due for an upgrade but I guess she gets it instead if me. But that's ok. I like my phone. Even though I'm getting close to running out of memory.
That is exactly what mine was doing. It would show 90 percent charged and shut off. I would try to restart and it would show less than 1 percent and wouldn't fully start. I had to plug in the charger to get the phone to turn on, and it would show 30 percent and jump to 100 percent in about a minute with the charger plugged in.
I had to replace the battery. Now it lasts up to 2 days before I have to recharge.