I have both arms but a stroke has made my left arm and hand half useless.
These mixing bowls stay put without holding them https://smile.amazon.com/Navaris-Stainless-Steel-Mixing-Bowls/dp/B085TLWSR7 Heavy ceramic bowls are good too.
A rocker knife https://www.webstaurantstore.com/t-grip-3-3-4-adaptive-rocker-knife/542847124884.html is a godsend.
A cutting board like this https://www.rehabmart.com/product/swedish-cutting-board-699.html is or should be in every one handed kitchen.
There's a jar opener ... thingy that mounts under a cabinet for opening jars. Also, a battery powered one handed can opener is probably in order.
Get a "spreading board" so you can spread butter or mayo or jam one handed.
OXO POP storage containers like these https://www.target.com/p/oxo-pop-5pc-airtight-food-storage-container-set/-/A-15295140 can be opened and closed with one hand. I have a bunch of them and love 'em.
I don't need one of these but for some people I can see it being very useful. https://www.performancehealth.com/folding-pan-holder
An OXO chopper https://www.oxo.com/chopper-371.html#could be handy.
And of course, a stand mixer.
I'm sure there will be lots of rehab with a lot of experts but both of you might want to look at this: https://www.saebo.com/blog/tips-one-handed-cooking-stroke/
PS - if she doesn't already know that the best way to separate eggs is with your hand, let her know.