I love how consistent she is with her Morticia style. It takes a lot of balls to hang on to it, as it's something that can easily go horribly wrong (think Helena Bonham Carter) or just over the top harsh and turn unattractive. Also, it's not a style you choose if you want to secure a place on best dressed lists.
What I think keeps Eva's outfit choices from going haywire is that they are so grounded on her personality: her style always accentuates it instead of hiding it. When you really know who you are and dress according to your own taste, you can't go wrong, no matter how daring you are.