Cinders, All I can say is "well, well, well...Mother Karma is catching up with the ow." It's not guilt that's got her, but the fact that she's finding out that the fantasy life is starting to crack and the facade that she's so carefully maintained for so long is starting to crack under the scrutiny of family and friends. People are not pussy footing around her any longer and you know what? She needs to hear what people think about her and the situation. Let's face it, she's not a saint by any means.
I now firmly believe that she wanted you to be a part of the "happy couple" in order to convince others that you were okay with the relationship that she has with your husband. It's not that he's incomplete, but her...she needs your blessings and friendship in order to win others over. I do hope that you've maintained your stance on not participating in her little games of deceit.
Let the woman cry...crying is good for the soul....and just maybe, she'll realize what she's done and get the heck out of your h's life so that he can return to his family.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.