She’s the ships counselor, who at any moment may need to have deeply personal and unofficial private conversations with anyone in need. Those discussions are officially informal. Thus she maintains a casual professional appearance.

It’s not jazzersize, it’s public lounge wear, she is at ease to help aid her clients ability to transition to an at ease state.

While doing official duty on the bridge it is appropriate for her to dress in uniform, but those duties tended to be momentary, not planned, so a wardrobe change would’ve been an odd choice.