How do they style their hair and facial hair if applicable? How long is it? Do they frequently change this?
For the vast majority of the time Beau has her hair tied up in a bun. It was something her mother taught her to do at a young age and the habit stuck; of a morning she would comb it through, then tie it up when she went to play or work or train or… anything. Then she would return home, once again comb it through, and sleep - only to repeat the process.
Given her activity as she grew older, the bun becomes more and more messy throughout the day. Eventually that became habit, too; call it her human-side coming out that her hair no longer was perfectly tied up, but rather had strands falling loose which only worsened as the day passed.
She keeps on top of her hair still, though; ensuring she remains to comb it twice a day. She’s never cut it, either - so it’s safe to assume her hair is rather long.
How do they usually dress when not in armour? Do they wear jewelry? How important is style and fashion to them?
Honestly? She dresses in whatever she has. She owns a couple of high quality cloths courtesy of her mother but most of it is cheap, relatively neutral-coloured garments. Most of the time, unless she is sleeping, she simply takes off her outer shell and rests in her chainmail and/or her doublet.
She doesn’t have any jewelry of her own, though if she did she would more than likely wear it. As for style and fashion, it is something she admires but doesn’t necessarily adhere to herself.