missed biometric appointment after B2 extension

[VinodKan]

Hello, my mother visited us from India in June of 2020. Due to very high cases in India in 2020, we have decided to extend her stay and I have filed for one (I539) in October 2020 online (through USCIS website). I have not logged in into the website again because I was expecting a mail for her biometrics appointment. She left the country in April 2021. We have not received any letter from USCIS until then. Today, I logged in to the USCIS account and I see that there was a biometrics appointment letter for my mother, attached staying that the biometrics appointment should be fulfilled on 31st March 2021. I tried to call the USCIS to explain the situation and my next steps, the automated system says that if we have missed the first biometrics appointment, USCIS will automatically sent another appointment letter with in 60 days. no new attachments in the portal or in the mail. Its been close to 6 month already that my mother have left the country. My question is, what are her next steps, and will it be considered as she stayed illegally after her stay of 6 months? what is that I can do now, to avoid any extra processing or questioning or rejection if incase she wants to visit us again in the future. I really appreciate your help with this