I would possibly say that getting back to work would be better than moping round the house all day.
Everyone has their own way of grieving and the harsh fact is that life does go on after miscarriage.
So long as she isn't bleeding profusely, and she wants to go back and her job isn't strenuous, hopefully her supervisor/manager has been informed, so that if she wants to go cry, or jsut feels crappy, they can be sensitive to her needs, and most importantly she wants to go back, I think its great and say she should.

I lost my son at 20 weeks two weeks ago. I stayed home for a week and than thought I could handle work. I returned on a monday and made it half way through tuesday's work day before I threw in the towel.
The fact that you state harsh facts causes me to think that you have never had a miscarriage or that you didn't really greive for yours. It is important to let yourself feel...and when you feel up to returning to work, then do it. But don't try to push yourself to perform. It only prolongs the grieving process.
Losing a yet unborn child is no different from losing one whom you birthed living.
It is no less real a loss of a child.
Be sensitive.