Of course Ciri's outfit is sexualized, idealized and symbolic. In every videogame ever the devs must make a choice whether they showcase their characters in a realistic or idealized fashion (males AND females!), and usually find a characteristic middle ground in serious games (at least in the west, Asian games tend to be kinda silly). Also, limited ressources lead to each character usually being depicted in a single set of clothes that has to work in each situation (just ask some Skyrim modders how hard it is to create detailed, beautiful and non-clipping outfits comparable to what Ciri wears. I expect several full workdays of a skilled professional for such an outfit).
In full realism mode, Ciri would carry around several bags with personal belongings, would wear rather ragged, unfitting clothes due to being on the run, would probably have lousy hair, bad teeth, smell of sweat, dirt and blood. I exaggerate, but especially in a medieval setting, personal hygiene is hard to come by, and her fate during the last months/years certainly should make her look more like a Syrian refugee than the semi-model she appears ingame.
Instead, Ciri's outfit symbolizes the following things:
- It's a traveller outfit, not a combat suit. Ciri was ever on the run until she reunited with Geralt,Yen & the rest. Only then direct combat/fighting back truly became an option.
- She still cares for her look, hasn't given up herself, is still more than just a desperate fugitive. The wild hunt hasn't broken her yet.
- She is supposed to be relatively attractive. To be perceived as such next to Yen and Triss by players, she can't wear rags.
- She survived by blending into crowds, not by drawing attention and looking threatening (and full military gear on a young women draws attention!)
So to sum it up: She has one iconic outfit due to budget restrictions, and it first and foremost has to tell us things about her. Being plausible in every situation is secondary.
I also heard on several occasions (e.g. from Youtube channels about historic weapons such as scolagladiatoria, Lyndybeige and others) that leather armor is vastly overrated in video games compared to it's historical role. A leather jacket thin/flexible enough for daily use offers almost no protection.
Chainmail instead was awesome against everything but blunt damage and very advanced, well aimed projectiles. Nothing metal-free ever came close. Padded armor was decent if it was several centimeters thick, but then it was exactly as clumsy and impractical as chainmail. Knights in real combat combined both, but they didn't wear this combo every day. Roman soldiers had to be forced to always wear their mail, and often didn't in the late ancient period when discipline bagan to drop.
So IMHO, the first time Ciri would have sensibly considered changing into light chain and some padding underneath (IMO the best combo for an agile swordfighter) would be the battle of Kaer Morhen. But there's no shop or real blacksmith there, and we can't expect that there's a fitting armor lying around. Also, the plan was to keep her out of combat.
This leaves the battle preparations in Novigrad as first real chance for her to aquire a proper combat suit. It would have been awesome if they had replaced her blouse with chain instead of the fur collar, but well, they had their reasons I guess.