[Not just regret. Bald, unbridled disgust. It's a disgusting, twisted thing, to separate an angel from its Grace. They called Anna a more disgusting abomination than even the stains that called themselves demons- and why? Because it wasn't right. An angel belongs with its Grace, anything else is a perversion of God's design.

It may have taken dying and coming back without memories to see it, but the fact that they did that to him at all was repulsive.]

We saw Castiel, moments after killing me, twisted and bloated into an unholy abomination, rise up and declare himself God.

[It still terrifies her a little to remember. Not just the vision, but the infinitely more real memory of Castiel's deadened eyes looking into her, hollow and horrible, of how empty and disturbing he was just to be in the room with, how she knew without knowing that it was no longer her brother. The moments of terror just before she died- she still remembers.

Seeing that creature again, and committing such appalling blasphemy that she wants to flinch even repeating it... they all lost their heads.]