I take a multi-vitamin plus vitamin C with rose hips, it's very good for the immune system and the lungs. I also take glucosamine, chondroitin with MSM and find that it does help with the achy joints. I also take an omega 3 fish oil, which my doc recommended for raising my ldl and have actually felt better since I have been taking it.
As far as what to say to your Grandmother, who really does mean well. Just tell her that you are taking vitamins and are looking into some others to try, and thank her for the advice. We all like to feel useful and she probably doesn't know how else to help.