@stupida, thanks a lot for clarification. Yes, it is mentioned in the case received letter and they also charge $85 biometric with application. In the received notice they have biometric section, and they said they might call you but not fully sure about it. It is also mentioned here.

https://www.uscis.gov/i-539

I found about days on goggle search (lawyer site) and it seems true.

https://www.uscis.gov/news/alerts/covid-19-delays-in-extensionchange-of-status-filings

Thanks for documentation reminder. Yes, I will contact USCIS if my parent cannot go back and seek suggestions. This covid situation is becoming hard and as u said earlier, I will try to enjoy her company as long as it lasts..............