1. If she can pick up her immobile hand and lay it on the yarn as well as on the work, that can give her some control over the tension. I don't normally wind my yarn around any fingers, either when I knit or crochet, so I know it could work.
2. If and when she gets back a small amount of mobility, a hair scrunchie around her palm with the yarn run through it might give her enough "grip" to make it easier.
It's possible to knit "shepherdess" style with a long needle held under one arm, handling the yarn and work entirely with the other hand. Something tells me it should be possible to do Tunisian that way, too, or possibly to use a long Tunisian hook under the nonworking arm (using it as weight only) and maneuver at least small things with the working hand.
Where there's yarn there's a way!