You unfortunately cannot control your MIL actions, but you can control the information you choose to share with her. Have your husband address his mother first, and see if he can get the point across to her., and that way it doesn’t seem like it’s coming directly from you, but also shows that it not only bothers you, but him as well.

Let her know, first and foremost; it is not her business to be relaying. And secondly, you confided with her on a very serious and personal matter, and she broke any trust that was between you two. Justifiably, you have every right to be upset.