Your phrasing came off as you not liking her skin tone, but I hear what you're saying. It also is realistic to get a tan after a year+ of costant sun exsposure without skin protectants. She could also develop sun bleached hair especaily with the constant exposure to sea water due to her fishing accelerating the process, though her being a brunette originally the hair would most likely be dirty-blonde, but I assume they exaggerated it for the story.
Salt water can definitely lighten someone’s natural hair color (not bleach it like in a salon or from chlorine in a swimming pool), so I agree that our MC’s hair color was exaggerated to a degree, although maybe it’s also related to where she was and maybe getting contaminants from the Land of Tragedy. Also, I agree that tanning from natural sun exposure (and burning) can darken your skin tone. Not every pale or paler person can tan or burn, but there are people like the MC who burn and then tan (like me, for example).
Personally, because her tan is so light (in my opinion), her skin tone is actually completely reasonable for how much time she spent outdoors in limited clothing for a year. I would have raised my eyebrows if she was two to three shades darker.

ugh im not sure why we have to make the mc tanned as fuck with her hair colour different, and shes so easy to trust people tbh