If you add a bag of salt only when necessary rather than filling your brine tank as full as possible, it's doesn't much matter. However, because this is your Grandma whom you don't live with, I suspect you will be filling the brine tank - If that is the case, you pellets, rather than crystal. The pellets tend to be a bit purer and resist crushing better.

Hey Alice,
OK great, that makes sense. I use to fill-up the old brine tank for that reason but after reading a lot of the threads on the site I discovered that was a bad method. With the new softener I plan on just adding 2 bags at a time cause you got me set-up to soften so efficiently & not waste a bunch of salt.