How intense should her workouts be during first trimester or later on? What activities are recommended which are not invasive and won't pose a threat to the baby?
I think anything she was doing before getting pregnant is safe to continue. I don't think they recommend starting any new training. There are also pregnancy workout videos. My wife still does though a lot.
No horseback riding or bike riding, no skating, nothing she can fall down or be thrown down doing basically. Towards the end yoga and walking or swimming are about it.