"The Darkness and the Light"- was it true to character?

Yes, I think it's in character.

Regarding what Kira says to Prin, I think she really believes it and it's logical based on her character that she would. That doesn't mean it's the whole story. People are complicated and often contradictory as hell.

As for "endangering the baby" a) I don't think she did and b) who cares anyway? It's a TV show!

I like this episode a lot and I think it actually did moral ambiguity and complexity better than some of DS9's more celebrated episodes.