Joan Aiken is an odd duck, agreed. But then I think bookelfe is also a bit odd in the duck department for calling The Whispering Mountain a Gothic- if I didn't misread that entry completely. (She was talking about another book that does indeed sound gothicky.) tWM is just one of Aiken's James III series, weird by definition: with a Prince of Wales who speaks highland English and a bunch of Welsh villagers who sometimes speak Welsh, usually speak Welsh-English, but mostly speak Yoda. "Weigh no more than a feather, this boy do! Help to you he will be, too." "Regular cloudburst there must have been up at Pennygaff. Owe all our lives to you, we do, Owen, I reckon!" I can't believe Lucas' screen writers were conversant with Welsh-English word order and did that deliberately, so I must assume Aiken Got It Rong. Mind, my standard for these things is The Owl Service, and maybe it shouldn't be.
Then read The Islands of Chaldea, DWJ's last. Mh, speaking of odd ducks: she and Aiken were two of a kind-- both regard loss of close relatives as no big deal. And Wynne Jones is generally much less genial. Why yes, I could guess where Ursula took over: it was when the signals for a happy end came so neat and quick. DWJ would have been much more problematic about it.
Time for something completely different: probably continuing with The Steampunk Trilogy which is a bit more like, except for that steampunk obsession with whores and brothels. The absence of which is one sign of good steampunk, in my book.