Stick to the facts. Just say you know what you know and have proof.
You can't appeal to her common sense side right now. She'll be too hopped up on anger/fear/embarrasment, etc. You have to wait till all those emotions run their course then when she's calmer you can talk about family, being a mom, etc.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.