It isn't a medieval world though.

It is a fantasy world that merely resembles medieval Europe. You can see this in the way she cast freaking magic.

And even back then people dyed their hairs, yes including blue.

1. Hair dye actually has a long history.

2. Magik

Magic? Nothing to blink twice at!

Hair color that's fun for the player? Realism ruined.

blue hair = 5*5+10+10*5*5*10

Have fun!

Hair dye DID exist in medieval times tho, and in fact, even ancient Egyptians dyed their hair

Why is the LITERAL WIZARD not a tradwife lmao

"It" might not even be human, and could be part of a species that naturally has blue hair pigment.

"It" is also a fantasy character casting magic spells - it wouldn't be far fetched that aesthetic magic exists.

Prestidigitation.

Urine showers with woad shampoo, it's called fashion, look it up