It is very difficult in life to not be, -ist, be it racist, sexist or whatever. If we were all exactly equal in everyway, height, colour sex etc, thinks would be fairer, but we are not and things aren't. I am a white bloke with a 20 year old Son and a 4 week old Son and this is my opinion; The lady is pregnant and that is a medical condition. In the early stages of pregnancy physical and physiological changes occur which could affect her flying/decision making skills temporarily and worse still without warning. If she is off with full pay then she should enjoy it while she can. She may of course feel that it is her decision but others lives could be at risk so the medical aspect has to come first. i think the first and last 3 months rule (if it is correct) is probably quite a good one, but again, pregnancies are funny things. Maybe the pregnancy wasn't really planned and she is sub-consciously rebelling against her unintended lack of choice. We all sign contracts of work and I presume that this was covered in hers. i wish her all the best as a Mum, and can only say that I don't have an answer only an opinion.
Remember opinions are like arseholes, everyone's got one.