Actually, I've always jokingly referred to Kreia as mommy, because she's just so motherly toward the Exile the whole damn game. I don't approve of you being too lightsided. I don't approve of you being too dark sided. I don't like the way you've been hanging out with all the girls (if you're a male Exile).
So her wanting SO much for the Exile (and I truly believe she loves you, too), but abandoning Brianna, w/o a single thought seems weirdly inconsistant to me. Sure, the Exile's a wound in the force, and Brianna just you run-of-the-mill Jedi, but, what?
she does now that you mention it