I don't think she uses hats in all of her designs, or that she really needs it. It would be cool if she did though.
I always thought of it as sometimes she has it on and sometimes she doesn't, not unlike how, say, Jason is sometimes shown with his helmet on and sometimes shown without it and wearing just the Batmask on his face. Zatanna has similarly been shown to wear her hat on-and-off. Actually makes sense, tbh, given people tend to do that irl.
