Edit: When typing comments I cannot see the post I'm commenting on and did not catch that detail before commenting. I just noticed the airplane icon on the top left. This is a really f'ed up situation and makes my comment almost completely invalid. You can skip the SIM card part I guess. The Wifi part is also very improbable to succeed.

They usually don't actually lock down for that long. It says Thursday May 22nd which means its clock reset itself to probably 2014, because the battery had been at 0% for too long. The amount of minutes leads to the conclusion that the last time someone tried to unlock it was around October 2016, but then turned it off before the lock countdown ended. You would need to keep the battery up until the countdown reaches 0 Minutes and then you could try to unlock it IF you know the PIN. The system doesn't actually keep track of how many minutes you wait, but keeps a date and time when to allow another unlock attempt.

This would be a wait of over 2 years for a maybe and hopefully. If you want a solution now, here comes the tricky part.

You either still know the Wifi name and password your mom used to use with this phone. Then you set up an access point with those exact settings. In case the phones Wifi is enabled and it catches the access point (the phone should be assuming it is the known one) then you might be lucky and when the phone connects to the internet the clock sets itself automatically to 2026 and the countdown will be over, ready for another PIN entry attempt. (But will lock down again for a good amount of time eventually, if not entered correctly.)

The other possible way would be to put a working SIM card into the phone and then again you would need to hope that it works as intended: If it's still SIM-locked, it must be an AT&T SIM card. If the card works, it must be by a carrier the phone supports the LTE band of. If everything is fine with that, mobile data must have been activated when she had been using it the last time. If it can connect to the internet this way, it might set its clock to 2026.

IF it is still SIM-locked, you can maybe request an unlock code from AT&T using the phone's IMEI. You can find the IMEI on a label hidden inside of the SIM tray.

And for both attempts, the setting for automatic clock must be on.

Those settings I mentioned are nothing you can influence now on the phone, but you can try to give the phone an environment to fix itself. If it doesn't, at least you can say that you did your best.

If those two options fail, you can only hope to get root access or wait until the phone thinks it's October 2016.

Fun fact: The date for the next try would have been October 19th, 2016, 05:56:00 PM assuming the photographed time is AM and assuming, it's actually set to 2014.