Hi To reset your tablet and unsynch the previous owner's details follow the instructions below:  Turn off your Android device. ...  Press and hold the "power", "volume down", and "camera or home" buttons simultaneously. ...  Release the buttons once your Android device is powered on. ...  Scroll using your "Volume up and down" button until you find the "wipe data/factory reset" option.
You'd have to reset her tablet then  Turn it off .  Once turned off, Press and hold the "power", "volume down", and "camera" (or home button if no camera button) buttons at the same time  Release the buttons once your Android device is powered on. ...  Scroll using your "Volume up and down" button until you find the "wipe data/factory reset" option. Hope that helps
hi  could you confirm that the battery holds enough charge? If not, try charging it for at least 15-30 mins, then attempt to turn it on.  does the screen light up when you charge it? if not try changing the charger and or the charging cable. let me know if this helps
hi Im not sure if Samsung allows changes in the bubble color in their SMS app since it's been yrs since the last time I've used one. I recon there are many custom 3rd party SMS app such as Google Hangouts, ChompSMS, QKSMS and more that you can use as your default SMS app to give you customization flexibility. Hope that helps/ Thanks :)
hi I assume you've tried other SIM cards and have confirmed none of them works in the device. and that you have tried cleaning the SIM terminals. has this been water damaged in the past? (or has moisture or small amount of water seeped into the internals - i have recently repaired a samsung S3 with the same issue and found it was due to water damage)
try pressing the test fire button or shorting the terminals and it should flash (while not connected to your camera). If it does, then you know your flash works, if not try looking into your camera settings.
 can you fix it? Yes of course. It should be easy. Much easier if you know how to solder, otherwise you would have to twist the wires to connect the broken ones. kindly post a picture here and I will give you step by step instructions on how to fix it.
I have used the Asus (ZE551ML) before and have experienced tons of issues but not this one so I have to guess, what I would do instead is try disconnecting the battery and reconnecting it (soft resetting it). Asus is known for their buggy OS (their customized android even destroyed my zenfone 2 lcd during an upgrade) and buggy apps even on PC. so Im hoping a soft would be sufficient. and make sure you dont update the OS. I learned that the hard way. Let me knw it that helps
hi Just to confirm, (1) you're able to get past the POST /bios screen right? (2) if yes, do you have the Windows installer CD/USB with you? (3) if yes, plug it in/insert it and restart your machine then go to bios, choose the CD/USB as the booting device, (4) if it loads then try repairing windows, you will not lose any files in this procedure , but you may lose your programs and would need to reinstall them. (5) if that doesnt work, it could be a hardware issue let us know what happens thanks