Need help with Icloud

Hi, my grandma recently upgraded to the IPhone 8 from her IPhone 6 and gave me her IPhone 6. The only problem is I can't restore the phone because she doesn't know her ICloud password or the password to the email that she used to create the account. I tried using security questions but she doesn't know the first celebrity she met. Obviously I have the date she was born so I'm not lying. Help would be great and I will provide proof if needed. Thanks.