I requested a B-2 visa extension on September for my mother, she has to stay until may 14, so she is already 1 year in USA as a visitor, but due to covid-19 I am worry about her health, she is 74 years old, with dementia and diabetes my father is the one who takes care for her, He is citizen. Is possible to get a new extension while everything is safe here or in our country?
To answer your question, yes, there is no limit to the number of times status can be extended during one stay (note that it is the status that is extended; visas cannot be extended, since visas are only for entry anyway), and it is possible to apply for another B2 extension of status before the current extended status expires. Of course, the chances of approval of an extension of status goes down with each additional extension. The fact that she has a US citizen spouse in the US also may make it likely that she will be denied for immigrant intent. But at least an application for extension of status (filed before her status expires) will allow her to stay while the application is pending, which can be several months, so it will buy her more time.
As some comments have noted, if she intends to keep staying in the US, it would be better for her to not apply for extension of status, and instead apply for Adjustment of Status to get a green card in the US through a petition from her spouse.