If you mean the films, her character is absolutely inconsistent, as the result of taking one person with her beliefs, qualities and feelings, and suddenly changing her into some other character, rather unrealistic in itself.
If she loves him, then she will love him despite being criminal, because she knew him to be murderer when she married him. If she is not stupid, and she never seemed before, she will understand obvious things and will not do stupid ones. If she is a decent human being, as she seemed to be, she will not betray her husband in the most difficult moment of his life, even if she didn't love him anymore, because it is mean and unfair.
I don't know how to rate her.
As to the novel, I don't really think something's wrong with her. It's time to grow up at last.
BTW, Lavinia, what prevents you from reading the novel?