Question : Is it possible to apply for PR for my grandma who is 94 and currently on a long-term pass.
This question is bit complex than it appears. First of all you need to understand the correct scheme under which your grandma can apply.
Aged Parents of a Singapore Citizen
This is the only scheme under which your grandma will be able to apply for PR. However that means, you can not apply for her PR as you are a grand child. So your parent will have to apply for her PR.
Her Son / Daughter must be a Singapore Citizen
To be able to apply for PR, her son / daughter who is filing the application must be a Singapore Citizen (A Singapore PR can not apply for PR of parents!)
Now the PR application for aged parent of a Singapore Citizen is a sponsorship scheme, where the economic capability of the sponsor will be taken into consideration. Considering the age of grandma to be 94, your parent are likely to be in the age group 65-75. So are they economically active? If not do they have enough investments to support grandma?
The last point you need to consider is the age. At 94, grandma is not likely to get any insurance coverage, as most of the companies stop coverage by then (or the premium become almost unaffordable). But at that age, medical problems are also there. So authorities are likely to be concerned about the cost of medicals and its likely burden on public hospital.
Considering all above points, I think its not going to be easy for you to apply for PR for your grandma.