Cersei has always been a complex character. She’s dealt with two members of her family dying, and her obsession with getting revenge on Tyrion has cost her dearly. There are times in the books (for example when she burned down the Tower of the Hand) where Jaime thinks that Cersei looks and acts like Aerys, just when he was watching something burn to the ground. Now, Cersei also thinks that, since Jaime got his hand cut off, he lost a part of himself, and that now he’s a changed man and so not to be trusted. As I said before she is a really complex character.
Gosh, I wish I had the time to find the exact passages from the book right now and tell you more about how I see it from my point of view. The sure thing is that I don’t believe she’s going mad, and/or -gods help- definitely not being redeemed or anything.
Come off anon, ask me and if I have enough spare time, I’ll do it :)