Was the Marsh Girl real in Where the Crawdads Sing?

In Where the Crawdads Sing by Delia Owens, the Marsh Girl is real. It is the nickname the townspeople give to Kya Clark, a girl who was abandoned by her mother at the young age of six. She watches her siblings leave too, as well as her father. Left all alone to fend for herself, she learns to live off the land while she becomes ridiculed by the townspeople who assume that she is wild, untamable, and unable to acclimate to social norms. Since the townspeople know very little about her, they turn her into some mythical creature that many assume is not real, but she is.
As she grows up, she starts to interact with boys her age. One of them, Tate, urges that she publishes a reference book on shells from the swamp, which she does. She becomes a successful writer, but in the meantime, she is also accused of murdering Chase Andrews, another boy her age who she spent time with while Tate was away at college.

"Marsh Girl" is the nickname given to the protagonist of the novel, Kya Clark. Abandoned by her entire family and eluding truancy authorities, Kya learns to make her own way in life from a very early age. She relies on the marshlands near her home to provide everything she needs, from supplies she can use to trade for food to companionship via the wildlife.
The townspeople look upon her with scorn, assuming that she is wild and untamed—unfit to live in typical society. Thus, the people deem her the "Marsh Girl" and toss her to the outskirts of life, never reaching out in kindness. The only people who seem to really see the strength within this girl are Jumpin and his wife Mabel, who provide basic food and supplies by "trading" for Kya's collections and developing a relationship with her over time, and Tate, who becomes romantically involved with Kya and then leaves her to study at UNC—Chapel Hill.
Kya embraces the strong image of the Marsh Girl and becomes an accomplished scientist and artist specializing in the marshlands of coastal North Carolina. She publishes books on the subject and amasses specimen collections unlike anything anyone has ever seen. Thus, Kya transforms the image of Marsh Girl which was meant to be demeaning and channels it to instead become the Marsh Girl, an expert in the sciences of marsh life.

The Marsh Girl is indeed real. It's the nickname given by the people of Barkley Grove to Kya Clark, the young lady who's been leading a hand-to-mouth existence out in the North Carolina marshland ever since her family abandoned her when she was six. But the local townsfolk don't know a whole lot about Kya, so they turn her into some kind of weird boogie-man figure. Over the years, the Marsh Girl becomes more of a local legend than a real-life human being: a strange, semi-mythical creature that blurs the boundaries between reality and fantasy.
It's this legendary quality of the Marsh Girl that draws Chase Andrews to Kya. He's fallen in love with the legend rather than the actual human being behind it. To a spoiled young rich kid like Chase, Kya is like no one he's ever seen before, and he's utterly fascinated by her. But like everyone else in town he never gets to know the real Kya: the poetic, sensitive soul that lies beneath the wild, primitive exterior.