I believe that method of consumption is just as important as strain choice, in my case even more important. I have severe spinal chord injuries and find everclear tincture (using the Green Dragon Recipe) to work much more efficiently than smoking or vaping any strain. The best strains I find for pain are Dutch Passion Blueberry and Delicious Seeds Fruity Chronic Juice(both photoperiod strains though). The autoflower has some really good stock bred for medical effect including the stone dragons(have 3 almost ready to chop) and moonstone.
Good luck, hope your wife finds the ultimate arthritis control with cannabis. My aunt has heavy arthritis and she finds canna helps her sleep especially smoked in the form of hash.