Hi, and welcome to the UK community.
When she first set up the tablet, she would have had to enter some credentials, email, and password. Does she still remember these?
If she's forgotten her password to unlock the device, then she can boot to recovery menu and reset the device, but as mentioned, she'll need to know the email and password used during initial set up as she'll need these after the reset.
To proceed with reset via recovery menu
Plug into a working PC or laptop or other Samsung device
Turn the device off, then press the power button and volume up at the same time until the Samsung logo appears. Then let go of both buttons. You are now in recovery mode, scroll down using the volume buttons to reset the device, and confirm with the power button. Follow all on-screen prompts.
When reset, enter credentials as mentioned before.
WARNING: You will lose all data. Hopefully, she has a backup?
If she is unable to boot to recovery menu due to a forgotten password. Then, the only other course of action is to take the device to an authorised Samsung centre and let them unlock it for her. She'll need to be able to prove the device is hers.
https://www.samsung.com/ca/support/mobile-devices/what-can-you-do-if-you-forgot-the-pin-pattern-or-p...
