Hey there! Nice to meet you!
Based on your description, this indicates that your mother's account is blocked due to the system detecting unusual activity. Her verification method will not work until the account block expires.
Since you mentioned that your mother has already waited 48 hours and the problem persists, she may need to wait a longer period, exactly up to a week, before performing another password reset, as stated on the official Microsoft website:
Important: Please make sure not to attempt to sign in or reset the password during this timeframe (1 whole week), as this may reset the lock period.
Furthermore, account blocking is a fully automated security measure. According to the official Microsoft website, support will not be able to assist you, as they are not permitted to send password resets, access, or even change any details on the account:
Thank you for your understanding!
Best regards,
Darhyl