Let's just say that Solstice Wood is not Patricia A. McKillip's best work. McKillip usually writes highly literate fantasy in a vaguely medieval period, such as Alphabet of Thorn. Quite often, there will be well-placed illusions to Celtic myths and traditional fairy tales, as in Winter Rose. Solstice Wood, unfortunately, is neither terribly literate, nor does it feature anything well-placed. It felt like a hodge-podge of Alice Hoffman's Practical Magic, any number of insipid novels prominently featuring knitting or quilting (and no, I'm a knitter so I'm not knocking fiber arts), and teen fantasy centered on how much someone wants to be a witch/fairy/changeling.
The other problem is simply one of structure. The structure is a hodge-podge too. Though the protagonist is meant to be an oddly unlikable young woman named Sylvia, the story is told in the first-person serial, meaning that everyone, from Sylvia's equally un-likable grandmother to a fairy changeling gets a chapter. Sylvia only gets a small handful of chapters in which to establish her role as the protagonist. The result is that the narrative, which is slender at best, has no core. Pair this with the absolute triteness of the conflict and ending, and you've got a book that it's pretty hard to care about.
And now, I think I'll just leave it at that and say that, in the spirit of niceness, I don't have anything more to say.