JD - changeling is only wrong if one assume that no couples has more likelihood to have boys than girls. I am not a biologist, but i believe that is wrong.
Nevertheless - this is completely offtopic.For the riddle, just assume the women is question give birth to boys with probability 1/2 irregardless of her history.
Snowbird - best numerical estimate so far! i would say 1/3 was the obvious answer. Nevertheless it is not the right answer.
Albert - Well congratulations! I actually thought how it was with you and your wife last week when i read a "motivational" story in the WT!.
An open mind is the greatest danger to a cult - irregardless of what she choose, i believe she will have a far greater understanding for why you have choosen otherwise.