I think it was a conscious choice by CDPR to make her seem more like a daughter figure in the game as opposed to letting her show skin like Triss and Yen. Simple as that, really.



But if you want a lore reason, you could assume that her experiences in the books (I won't spoil anything), have made her somewhat more conservative when it comes to her body. I doubt that, tbh, but that's the best I can come up with based on what we know about her.