Don't know my mom's apple id to unlock her phone

Have you asked your mom for her ID and password?

See if she can recover the ID/password.

Apple ID - How to find your Apple    An iCloud e-mail address is an Apple ID.

Apple ID - Find              

Enter the Apple (iCloud) ID and click Forgot Password.

Apple ID - Manage            

Apple ID – Forgot Password            

You won't be able to unlock it if you have no iCloud/Apple ID information.

You are welcome. I'm glad support gave you the information. Good luck.