There is such a strong sense of familiarity, trust and respect Mary has for Thomas. I'm specifically speaking about the scenes where she so casually, takes her hair down in front of him like he is a life long friend. Where she hugs him and breaks down, and she quite literally has to be pulled off of him. And then, when she is telling everyone how much he's helped her, and gave her her new horse.
I think it's such a contrast to what Thomas is used to working with royals, especially when it comes to royal women and hair.
I'll never forget the scene in the book, when Anne invited Thomas into her room in the middle of the night, and her hair was out, and she was simply in her night gown. That was a power play by Anne, which Thomas realized. It was showing him that to her, he was less than a person. There was no need to be modest around him because she didn't register him as anyone of note - he is even compared to her fool in that moment. Looking for the page/quote where Thomas explains it...anyway. But why cover your hair for a man you don't consider a man of note?
With Mary it's different. The lack of gable hood, the familiarity, the ability to be around her at her most vulnerable moments. In contrast to Anne, who saw him as nothing, Mary sees him as everything in these small moments. Which is why I think he was so taken aback when she embraced him. Because he isn't used to that. There is no ulterior motive. The last time he was around a royal woman with her hair down, and she was undone, it was the emphasize how little regard she had for him.
Now, when a princess does it, it's to emphasize the opposite. That she sees him as a person and she is so grateful to him.
