Very Delicate and Uncomfortable Situation

[Kate]

I don't think we can assume that it was NOT some of those things the co-worker is worried about that caused the miscarriage of the pregnancy.
 For most people, living normally will not hurt their pregnancy, for others with certain conditions, it may be an issue. For example, my aunt had to lie in bed for 9 months twice, to have her two children, because just doing normal housework would bring on bleeding and miscarriage. Her daughter inherited the same condition.
Regardless, IMO, the OP should go with the "my doctor is OK with what I am doing", and drop the subject.

[fluffy]

I think you should sit down with her and have a very frank talk. Tell her that you feel for her, that you know that she is grieving, but that she needs to take a step back and stop the overly critical monitoring of your pregnancy. I would wager that she hasn't actually stopped to think about what she's doing. She's probably too enmeshed in her own grief to realize what she's doing to you. Let her know (gently) that she's stressing you out. If she keeps it up, you can try some of the other methods people in this thread have suggested.

I would also maybe close by asking what you can do to make this easier for her. Does she want to see things like sonogram pictures? Does she want you to change the subject if people ask about your pregnancy in front of her? This will have two effects: you'll help her feel better, plus then you'll have a better idea about how to act in front of her and won't need to second guess yourself.

A lot of people seem to have a natural tendency to monitor other people's pregnancies and offer up unwanted advice. I know I had to stop myself this weekend from telling a pregnant friend (who was complaining about how much she misses caffeine) that it really is ok to have a cup of coffee. Not my pregnancy, not my business. But a lot of people forget that. Add in the grief over her own loss and it's pretty understandable why she's been doing what she's doing. It's not right, but it's understandable.

[Redsoil]

Would it be at all useful to  try and see her comments, not as "accusing" per se, but as "caring".  I may not explain this very well, but if, each time she says something that you would normally find confronting;  to try and "translate" it in your own mind (no matter what it is) is "I care about you and your baby".  Basically, to reframe it so you can more easily ignore the comment and focus instead on the caring that prompted it?

May not work at all, but thought I'd put it out there.  Good luck with everything!