I have mixed feelings about JW books.
My dd loved them and they are well written. I think they're quite similar in a lot of ways to the growing up stories by Jean Ur, Judy Bloom etc that I read.
However there have been a couple of her books that I removed from dd-I don't think I've removed more than one other book from her so I'm not particularly fussy. The first was an early book of hers which portrays a romance between a teacher and pupil, very much from the romantic side. I suspect she cringes when she sees it! I hope she does anyway.
The other, one of her Girls in Love series, to me, for my dd, crossed the thin line between educating and glorifying anorexia. I may be slightly sensitive there having had a friend who died due to anorexia though.
Some of the books are great. I think Double Act is a really interesting character study, and The Lottie Project is another great book.
What don't I like? Well, I often find the main character a gobby little brat. Gobby little brat also has a tendency to "get together" (hint of romance in the future maybe) with the bully/unpopular (and often overweight) boy.
But that does mean I don't really care what happens to the main character, which is a bit of a failing in a book. I want to be rooting for them, willing them to win through.
So, yes, I think she does write good stories, but I don't necessarily enjoy reading them.
I don't know how true to life they are and whether a child in those situations would feel understood or not. The child I knew who was in that type of situation was far keener on Enid Blyton because they portrayed a happy life they could dream about, but that's only one child.
They remind me a little of Catherine Cookson books where the adults have issues, the children have issues, they're not totally resolved by the end but may be patched over with a dodgy romance.