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Is it a series? Possibly, Karen's Witch? A spin-off of The Baby-sitters Club.
http://www.amazon.com/Karens-Witch-Baby-Sitters-Little-Sister/product-reviews/0590443003
Was it a picture book? The plot sounds a lot like Martine a une étrange voisine (try a Google Image search to see the art).
"If it ain't broke, don't fix it. And even if it is broke, just ignore it and maybe it'll be sort of OK — like the environment."
No, neither of those fit. It was mainly text, which maybe an illustration every chapter, and I'm certain it wasn't anything tied to an extant series (I'll admit that I read Babysitter's Club and Sweet Valley books back then). Thank you for your guesses though.
Just to make it clear, the book was in English.
Trying to remember a kid's book, published prior to 1995 or so (I remember reading it in elementary school). The premise of the book is that a group of children are convinced that their next-door neighbor, an older woman with the right nose and warts, is a witch and she goes along with their ideas. I was reading Flying Broomstick and was reminded of the book, including a scene where they try a found spell for broom flight involving an ointment they concoct. The book was firmly on the side of magic not really existing, although I don't remember how seriously the neighbor was taking it all.