Hey there! Nice to meet you!
Since you mentioned that the account has two-factor authentication (2FA) enabled, does your mother have the 25-character recovery codes for the 2FA?
Important: If she has an active 2FA, the account recovery webform (ACSR) will inform her that the recovery request will be ignored.
If yes, please go to account.microsoft.com > Forgot Password > click "I don't have any of these" on both verification methods > click "Yes" on the 25 recovery code (if she has one) > from here, you will be asked to wait 30 days in order to update the security info and recover her account.
During this time, she will not be able to sign in to sites or services with her account.
However, if she does not have access to all of her verification methods and the 25-recovery codes from her 2FA, I'm afraid it is no longer possible to recover the account.
Thank you for your understanding.
Best regards,
Darhyl