Yoga definitely has many benefits if practiced safely during pregnancy. To name just a few, it tones the muscles of the whole body (to keep up with increasing weight of the belly, for a general well being and fitness and enough physical strength during labor), it helps to achieve a control over pelvic floor muscles (a fantastic tool for labor

and a great prevention for post-natal incontinence).
As yoga works not only on the "muscle" level, all the systems of the body - digestive, circulatory, endocrine, etc. are stimulated as well. And yoga also teaches us how to relax, let go of stress, tension, anxiety and worries which I believe is a gift from heaven in a pregnancy!!
It is nice of you to think about your pregnant friend and you can definitely share all of this with her. But it think that it is important that she starts doing yoga if she wants to. My experience is that things work better for us if we make the decision ourselves, rather than doing something because someone else has pushed us.
