<human>: I have a friend who I've known for about 2 years now.  About a day ago, through a variety of coincidences and people who don't know how to shut up, I accidentally learned a secret about her (abortion related)

I discovered this purely by accident and not because I was asking questions.  I don't care at all, but she was romantically interested in me, and I imagine I am probably one of the last people she would want knowing this sort of thing.  Normally, I would just pretend to know nothing and never bring it up again, but her friend is probably going to tell her I know everything, if she hasn't already.  I don't want her to avoid me or have everything become awkward.  Should I tell her I know everything and explain the circumstances?  How do I make it clear I don't judge her at all.  Or should I wait and let her tell me herself when she's ready, but then risk her misunderstanding?

Can you condense the text into a few key points?
<bot>: Accidentally learned a very intimate detail of my friends life.  She's going to find out I know everything, how do I approach this situation without embarrassing her?