Elphaba's wardrobe defaults to being very stiff, formal, buttoned up. She's very neat, put together. Particularly at the start of her time at Shiz--hair pulled back, more formal in her uniform than anyone else.
As she grows into herself and makes connections with Glinda and Fiyero she starts to relax and open up a little. Her hair comes down and I think at times the jacket comes off.
Her main look in For Good, has some elements of the change-- Elphaba has let loose and become more herself so you get the dramatic length and flow of her cape and overcoat/dress. But its still very stiff and closed off- neat and buttoned up and big lapels and formal feeling. She's still got to look put together (and now imposing) at all times to hold people off.
BUT the "As Long As You're Mine" cardigan is loose, oversized, very open with gaps in the weave. In her home with Fiyero, this is Elphaba actually relaxed and comfortable. Elpahaba without her armor on.
And then this is one-upped by her outfit as she's leaving Oz with him which is a super flowy guazy wrap thing far more delicate than anything else she's been wearing because she's not at war anymore.
