DW has one of those flexible rubber disks that fit over the lid on a jar. With that, you get a decent grip so your hand doesn't slip. She still can't seem to generate enough grip to open most things, so she hands it off to me. Macho Man never starts with the rubber thingie (first time I fail, I use the knife-as-hammer around the edges - that always seems to work.)
One time DW passed me a large jar of pickles to open. I dutifully grabbed the jar and twisted off the top for her. Unfortunately, the seal on the lid never gave way. The jar gave way. Why I didn't slice my hand to ribbons on all the broken glass, I'll never know and will always be thankful for. NOW, any large jars get the full treatment from me. First, the "knife" trick, then the rubber thingie, then slowly, I add pressure as I twist. If that doesn't work with reasonable pressure, I go back to the knife trick and start over. YMMV