Should I apply GC now for my 70+ old mom v/s continuing with visitors visa?

[KC_2014]

My mom is 70+ years old.
She has an Indian passport and valid US tourist/visitors visa.
I'm a US citizen with a US passport and Indian OCI.
I want to start her US Green Card process.

a) What are the next steps to start her Green Card process and typically how long is the start to finish timeline?
b) Is there any benefit in getting her GC now v/s continuing with tourist/visitors visa?

Thanks