I wonder if it's done on purpose, but in this kind of pseudo-historical setting, women would be required to have their hair up. Keeping it loose and unbound was the sign of a 'loose woman' and basically not something the average woman would do considering the effect on her reputation.
I noticed that every single background female character, like the mother of the MC and the panels with random nobles mocking the MC, all have their hair done up properly except for the MC.
I mean, I'd accept historical inaccuracy more if the artist hadn't shown that they KNEW hair was supposed to be in an updo and yet had left the MC's hair undone.
It's a bit of a pet peeve of mine. When it comes to hairstyles in such historical settings somewhere between the 17th and 19th century, women should have their hair done up, usually with a hat. And a man won't have bangs, as they'll usually be brushed back if there are any, leaving the forehead semi or fully bare.