Now these were good fluff, if one can get over the obligatory appearance of a loyal old black servant in various genteelly poor Tenessee families. The author, and the characters, are never unkind to the servant, never enjoy themselves mocking the servant; I choose to take one pie-in-the-sky statement that if the family had money, they would all go to college and the cook would earn a degree in Home Economics as serious. (Quite possible.)
It's harder for me to say why the fluff is so well-constructed. It isn't all well reasoned; the French duelling disguised-as-a-boy heroine in The Daredevil doesn't live up to her training, and I don't think the political plot much holds together, either. I would say the emotional reasoning is coherent, or that the characters are distinct and consistent (and peculiar and likeable). When characters are described as sweet and optimistic, they really are. The religious concerns are caused by and reflected in real behavior. The worries of the girl heroines, even when silly, are taken seriously because they're serious to the character; Phyllis is especially like that.
One steady trait, which sets them a little apart from both suffering-virtue Victoriana and from modern Mary Sue idealizations, is that the rich, kindly, spirited, good-looking heroine is recognized as a natural heroine by most of her peers. I suppose this is one of the things that makes them emotionally consistent. Certainly it's more fun to read than most idealized suffering, and it makes a lot more sense than perfect heroines who everyone dislikes for no reason (the Menolly disease). There's still plenty of trouble for a young headstrong person to get into.
The weirdest of the ones I read is The Golden Bird, which is a brave romance of chicken-raising, with a Methodist Dionysius in it. The dashing heroine discovers that the family fortunes are almost gone; she spends the remainder on a small mail-order flock of champion layers, and retreats to a shabby rural property; and the vaguely The Egg and I amusements of urbanite-learning-ruralism are leavened by a romance with a strange hero with funny-shaped hair who comes dancing out of the woods in homemade clothes. She calls him Pan, and is smitten by his resemblance to her champion rooster. Really, the pleasure in it is that the main character throws herself into everything, whitewashing or Gallus guy or anything, with happy allusions to any of her strengths;
Talk about Mordkin and Pavlova! To stand up and drive a team hitched to a jolt-wagon over boulders and roots requires leg muscles!
I also wonder if the peculiar Pan is a reference to, or memory of, Johnny Appleseed; the recent The Botany of Desire by sets him up as a harbinger of desire as well as horticulture.
The Elected Mother: A Story of Women's Equal Rights is a cheerful short story of work-life balance, and alliance between the genders and the generations. Tennessee remembers her as an adopted daughter and a devoted suffragist; I should think she was effective.
Project Gutenberg's collection of Maria Thompson Daviess' books
Google Books has The Elected Mother: A Story of Woman's Equal Rights
So wrote clew in Fiction (20th c.).