Has she had a visit to her physician or health care provider and has she been given permission to begin an exercise program and guidelines to do so? I think that would be a really important first step. It is partly important with the dystonia, because where she is experiencing it can affect what modality will work most safely for her.
I would want to make a case for including some yoga. I have worked with quite a number of people with sciatica and have found that (especially if it is functional) it can be very helpful. You might want to look to the work of Judith Lassiter or Elise Miller. Sciatica I also have seen quite a lot. I have not worked individually with anyone with dystonia, but have had someone in chair classes from time to time, and I know it is recommended.
Swimming might be good, but only if the neck it not involved. If it is the benefits of the swimming might be outweighed by the discomfort and possibility of injury. That is why it is really useful to get feedback from her medical advisors.