Hello. Very sorry to hear that.
Your best bet is to set a new Lock on the device and a new pin/pw will override the old lock.
Unfortunately, this facility has begun to fail on newer versions of Android on some models, (Google are withdrawing it) but its worth a try here :
www.google.com/android/devicemanager.
The thing is you would need the access to her Google account.
If you can find her Gmail address, Google can help if you know some saved memorable information or alternative phone #/email she would have added.
Try here:
https://support.google.com/accounts/troubleshooter/2402620?hl=en
Alternatively of course, your carrier should / would be able to help you, so best to try a store first in case the second lock fails.
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