why doesn't she wear the uniform?
For all we know, she does. That jumpsuit never changed much, so perhaps it was the official Counselor's uniform?
We have seen weirder. Crusher always wore a nonstandard jacket, Picard started wearing one later on as well, and all sorts of background and eventually also foreground characters wore the odd mustard jumpsuits.
What I'm saying is it seems unprofessional.
In comparison with the tights the men wear? I don't quite see it.