Griet is decidedly different from other girls her age in this novel.
First, instead of styling her hair, she always keeps it hidden and tucked into a full covering. Some other girls also wear head coverings, but Griet purposefully wears hers in such a way that it points downward on either side of her face so that she can keep her facial expressions hidden from people. What this means is that Griet is a deeply private person, very reluctant to meaningfully connect with people outside of her own small family. In fact, Griet is so fastidious about keeping her hair hidden that it becomes an important symbol of her reserved, cautious, even self-effacing personality. For Griet, showing her bare head to Vermeer toward the end of the story is a major upheaval and a serious display of intimacy.
Second, Griet is obsessed with cleanliness, and even the smallest displays of blood left under the butcher's fingernails or dust left around the objects to be featured in a painting really bother her. Her distaste for blood and messiness are brought up in the novel pretty much every time she encounters it! Of course, this obsession makes her an ideal maid, but it also makes her very critical of others, and it puts her personality into direct contrast with other, more relaxed women, like Catharina (whom we always see with a sloppy collar or with her hair messily poking out). The fact that Griet's ears are unpierced for most of the story also reveals her tendency to keep herself pure and clean, and when she pierces them for Vermeer, we understand how far she has fallen from her previously pure self (perhaps even more so than when she allows Pieter to take her virginity in the alley).
Lastly, although Griet tries to set herself apart from other girls by claiming to stay away from gossip, or "market talk," in this respect, she really isn't that different from her peers. When the talk is about someone or something she's interested in, she's likely to press people for details, and in the case of her mother's visiting neighbor who loves gossip, Griet even purposefully feeds information about the subjects of a painting into the gossip mill to serve her own purposes.