that it depends on the level of intellectual curiosity of the bio-mom. That sight offers good stuff, but it takes two to play. If it is anonymous, maybe she will think of it as spam and not think twice of who sent it to you. Or maybe she will think a friend of hers sent it.
IDEA-- Maybe you could practice sending (referring) it to a trusted friend or family member (tell them first) and see how the process works.

There's no way, even if it's anonymous, that she'll think it's anyone but you sending it. Several years ago I emailed an article to my husband's ex about new step-families and how everyone getting along for the best interest of the children was the way to go. Along with the article, I sent a note saying that I really wanted us all to get along, not just for the kids, but for ourselves, as well. Needless to say, she did not take it as it was intended, which was my reaching out an olive branch to her. She took it as a slam and responded accordingly.

I think one-on-one honesty is the best approach and if they are not mature enough to handle that from the beginning, then chances are good that they never will be. On the one hand, as mothers, I am sure we can all relate to how hard it must be to surrender your child or children to another woman to help raise, because good, bad or ugly, that woman will not be the same as you and her child-rearing ideas will be different. Maybe better, maybe worse, definitely different. It's hard for them to think of us as "mothers," even just "step" mothers, because they can't get past the territoriality of them being THE MOTHER. I think feeling threatened comes with the territory and I've always tried to take that into consideration. As a biomom and a stepmom myself, I can see it both ways.

On the other hand, I tried really hard in the beginning to bridge the gaps, be the bigger person, extend the helping hand, be understanding and flexible, etc. and all it got me was shit on. You live and learn.

In my opinion, I think it helps to think of her as their mother, rather than as his ex-wife, because then the focus is on the kids and not the fact that he was married before. I think you have to do your best to make it work initially and hopefully they will, too, but if they don't, you just have to live your life in spite of the ex and her manipulations and focus your energies on the kids and your own marriage/family situation.

~ Anne ~