I always find a skill system in mangas such as this kinda weird. Especially in cases like the archer one. For people in this world it is not like pressing a button in a game, you actually need to do smth, so how would it translate to accuracy or intelligence?
With strength or even evade you could think of it as a magical muscle improvement or a magic that would improve your reaction time, but it doesn't translate that well to other skills.
With accuracy you need to measure distance and point into your target it is more a matter of experience and practise than a body improvement. Basically you just need to train to improve this skill. Intelligence is even more of a swamp ground.
To sum up, why she didnt just train and don't relay on something so ephemeral as a skill point. It probably would be less effective but still better than to have an accuracy of a drunkyard at 3 am on Sunday in a biker bar.