Hey Indi

I find that discomfort in the wrists is quite common in beginning students and have found that emphasizing hasta bandha (hand lock) does a great deal for taking pressure off the wrists . Stacking the joints also aids in properly engaging the muscular support of the arms. Being mindful not to keep beginners and/or injured students bearing weight on their hands for too long (or at all, in the case of injuries) is another way the process can be eased for students.

Blessings.

Using a chair is probably the best solution, but most students are reluctant when they are he only on using them. A study, non-cushioned metal folding chair works best. In d.dog hands go to rest on the seat of the chair- if that is too much pressure, they go to the top of the backrest- as the wrist get stronger move the hands, lower or to the floor. On the floor, they can roll the mat up to use a a cushion for their hands- this angles and elevates the wrist into a more comfortable weight bearing position- there is also a prop called a wedge, it is made of heavy foam and about as wide as the mat that is made just for this purpose.

to build strength there is a simple tool that can be made with a wood ruler and a piece of string- tie a string through the center hole of the ruler (stack two rulers and tape together if they are very thin) and an object of suitable weight to the other end- leave about 18" between, to use hold in both hands and roll the object up then down.

I personally like students to use dolphin if they have problems with their wrists in down dog. If she's shy about modifications, you could have the entire class do it that way. I find that when students complain about wrist problems in that pose, they tend to have a lack of arm and back strength. That they are generally relying on their joints to do the pose for them instead of their muscles. Using dolphin FORCES them to strengthen their shoulders and back so when they move back to down dog they have the strength to express their pose in a healthy way.

I think the important thing is that you as a teacher experiment with your classes. Encourage the students to experiment and have fun in their bodies. We find the courage to be gentle and imperfect when we have fun in our practice.

As a side note, my downward facing dogs were painful before I started to engage my abs and lift UP and back instead of just extending my chest toward my legs. Too much grounding and not enough lift. It could be something as small as how she approaches it. But I wouldn't know unless I saw her in the pose. Good luck on guiding your student!