Offer her some light reading. There is a good deal of research on Reiki treatments, and I have summarised it in infographics on this site so nobody has to wade through the papers. Take a few to your next appointment. And listen to your doctor: the system of Reiki is a complementary practice for wellbeing, never a replacement for what she prescribes.
Yes, for sure. Many of my students are massage therapists or yoga teachers, and they combine the system of Reiki with what they already do. The one rule is to be upfront: tell your clients what you are doing, whether you are adding Reiki to another practice or adding another practice to Reiki.
Yes, in two ways: you can have a Reiki treatment, or you can learn to practise yourself. Neither removes grief, and we would not want to; it is part of us. What the system of Reiki does is help you keep moving through it rather than staying stuck, and the precepts give you a way to meet it each day.
No. I learned the system of Reiki before I was pregnant, and practising it while pregnant was one of the most wonderful things I have done: hands-on healing with the baby, breathing into the deep belly, and feeling connected to everything with a child who was already part of that. Treatments from a partner or friend are lovely too. If you are pregnant, go and learn.
I don't know, and nobody does. He would probably be flummoxed by some of what is taught in the West, and possibly by some of what is taught in Japan a hundred years and eight or nine presidents later. Things keep changing. All we can do is trace the teaching back as carefully as we can and try to keep some of that original experience in what we teach.