Hi sarabara :), I read your post and it really hit a nerve! For one, I also am a social worker and I am waiting for my new moissy ring set to arrive so I have had to think about how I will explain what they are if asked.
Long story short, I've decided that I bought moissys for several reasons, one being my dislike of blood diamonds and also because I love the way they sparkle.
I am going to tell workmates/friends that I traded my diamonds for these as an ugrade. Lying by admission? Not really, I don't want to explain myself and I believe I am entitled to my beliefs and I actually don't want to offend any diamond-wearing friends or co-workers.
Sounds like your co-worker is very much in love with the Canadian diamond story, don't feel guilty about her buying one!
I know there is a fine line between disclosing our beliefs in the workplace and maintaining our privacy..think about all the convos about relationships, childbirth, sex, drugs and rock and roll that women have!! I haven't always disclosed everything, becasue I have a right to privacy.
Enjoy your moissy, I'm sure she will enjoy her diamond!