The different options for the feeding tube seem to have widely different results for different people. I know that we had to experiment with a few different products to find one that worked (i.e. didn't cause nausea, diarrhea, etc). Is your grandmother being seen by a dietician/nutritionist? They are really good at helping to figure out a solution to these kinds of issues. The hospital where she is being treated should have one or more on staff - maybe you could look into that.
Best to you as you make your way through all of this. Your grandmother is lucky to have you!
Anita