Remember the Seinfeld episode where George did everything opposite from what he normally would have done... and things started going great for him? That should be you. Opposite Matt.
She's leaving you and running full speed towards D. Why would you help her with that? She has to start feeling some consequences for her actions. Helping her is only shielding her from the inevitable consequences.
M: A really long time. Crisis: 5 years. She's still worth it.
Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl