While I agree with FY on this for the most part, this isn't about her. This is something she is going to do. Has done. That's yesterday. Tomorrow is a different story. And this is about you and what you're going to do.
Honestly? I don't advise telling the family what she's doing. Won't change her. It may make you feel better in the short term; like you're doing something. But that won't last. It may get people to commiserate with you. But it's not about them, so that won't bring much comfort either.
I've been there. I'm glad I didn't tell her family what she was doing. I did confront her on one occasion when I found a valentine card. Didn't change her. Made her more defensive.
Only you can decide what you're going to do. Your boundaries are your boundaries, and as long as they are important enough to you to "die on that hill" there's nobody here that will tell you what to do.
As you deal with your pain over this, consider the future you. What would you want to see when you look back on your life about how you handled this? Seriously. Do you want to look back and say, "I caught her and I told everyone. They side with me even though she's gone!" Or do you want to live your life and make you the center of it?
What she does or doesn't do, is up to her. You have no influence at this point. You can hurt her emotionally, you can expose her, you can yell or scream. But that won't change what she's doing. These are her choices and she has to figure them out and live with them, the same way you do.
MLC is a b*tch. I don't think she asked for this either. But she has to see whatever she is doing through, at any cost. Have you noticed?
Peace, AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."