Dear Magan,
Good day!
Thank you for posting to Microsoft Community. We are glad to assist!
Based on your description regarding "Authenticator app problems" My sincerest apologies for the inconvenience this might be causing you, I would like to share some information with you, we have dedicated support team for Microsoft Authenticator related query. So, we would recommend you to kindly post your query to Microsoft Authenticator support Forum via Microsoft Authenticator - Microsoft Q&A Engineers who are dedicated into Microsoft Authenticator with rich experience and more resources can then assist efficiently. We believe they would conduct in-depth research on the problem you encountered and provide you with more professional assistance.
In the meantime, kindly note this is very sensitive and should not be discussed here in a public forum which is accessible to all Microsoft customers. We value your organization’s security and privacy; hence we suggest you to kindly contact your Sister's IT or school Admin to reset the Authentication method for your account. Admin can do it by follow Manage user authentication options. (If you are not sure who is her admin, can refer this How do I find my Microsoft 365 admin? - Microsoft Support). Thanks for your understanding! Your patience and cooperation will be highly appreciated. I wish you all the best!
Best regards,
Inema |Community Moderator