Terry Pratchett's young witch trilogy
For some reason, I couldn't enter 'T i f f a n y Aching', the lead character. I suspect the spam filter is blocking her first name to keep out bogus jewelry advertisements.
'Wrinkle' was the first book I thought of when I saw the subject under discussion.
You mean I missed a Ralph book? I recall reading a sequel to M&M titled 'Runaway Ralph', but I was well into my 20s when 'Ralph S. Mouse' was published. I hadn't heard of it until now.