Why did Lisa Edelstein not return for the final season of House?

With the ending of House, a lot of cast members returned to their roles in order to give some sort of closure either to their story or even just as more character development to House.

However, the sore thumb sticking out of it all is Cuddy, who did not return for this final season. Not even the finale.

Doing some general scanning and research, I keep coming across the same thing of:

"[Lisa's departure] came out of left field in my world, too," Laurie says. "I don't know who was privy to what at what time, but it was a great shock to me and everyone obviously misses her very greatly. Not only was she a great asset to the show as a performer, but we also just miss her company, because she is an absolute hoot to have around. She has been snapped up by another show and damn right, they'd be nuts not to. I hope she is having a great time, and I am sure she is."

Which is also the reaction of the creator, David Shore:

It was not our plan [to lose Lisa]. It is not what we had in our mind. Certain stuff got thrust upon us that I was not pleased with.

So the question is: What really happened for Edelstein that compelled her to leave the show and not even come back for the finale; unlike the other characters that have either been killed off (Kutner & Amber) or just plain left (Thirteen, Cameron, even Masters)?

I highly doubt a role on The Good Wife for 3 episodes, like I've seen in some places, was the sole reason for her departure and refusal to participate in the finale.