My first question would be, what does her physical therapist recommend (and if she doesn’t have one, why not get one?) It is great that she wants to be active, and yoga can certainly be part of her therapy. Motion is the lotion of life! My next question would be, are you already a yoga teacher? If so, why not guide her through some gentle chair yoga (Hatha): that might work for her. (Check out this
site for some suggestions on Chair Yoga for stroke patients.)
Having said all that, certainly she can do modified Yin Yoga. In general, Yin Yoga holds postures longer with relaxed muscles. You can do this with the Chair Yoga postures, but do not hold them as long as a normal Yin Yoga practice would suggest. Between 1 min (for upper body) to 3 minutes (for lower body) should be plenty to start. She can do the Chair Yoga postures like forward bends, twists, side bends for a minute at a time/side. For some hip work, should could try just crossing her legs, or doing Butterfly with her feet on a block, and eventually on a coffee table. Make sure she doesn’t only do Yin Yoga though, add some yang at other times so she gets both.
As always, ask her to be mindful and pay attention to sensations: both while in the postures, when coming out and even the next day. Pain should be avoided. Let us know how it goes and what you learn along the way. I am sure that there are many other people would love to hear what you discover.
Cheers
Bernie