She is actually aware how nasty what she's done, and kinda want herself to die because of it (she really think highly and caring toward Medea). But since the God loves her soo much, and Medea kinda want it herself (say the God

, you know, Medea ask to be Pscyche, right?) the God move their soul so Medea can be the one who die instead of Psyche. I seriously hate the God here. But at least I can forgive Psyche a little bit.
And the actual reason why the Prince choose Psyche is actually ... because of Psyche herself. Or, at least, her power. He want to be invisible with her power. Medea is just a scapegoat that he need.