Sara's Granny and the Groodle, by Joan Gill. Illustrations by Seymour Chwast (who animated the movie Yellow Submarine). Long out of print (it was published in1969), and with marvelous psychedelic illustrations both on the cover and throughout the book. Very Peter Max-influenced.
Sara (who always chews her food 100 times - or is it 92?) and her Granny go off on a trip in a taxi drawn by a goose. Who turns into a groodle (don't feed them after midnight is a rule that might apply here), who is rather bad-tempered. It all ends well, with Sara asleep in her psychedelic bed.
Used copies currently go for 75$ on Amazon.