This is hopelessly vague. This book really moved me about 25 years ago - does anyone have any ideas?
It was about a girl. I think she might have gone on holiday; anyway, she goes off somewhere and meets a new friend, whose name I believe was Miranda.
All I really remember is that they were eleven years old and by the end of the book the girl had decided that Miranda (possibly a ghost?) was sent to her to help her learn how to be twelve (which was the age girls grew up and got their periods).
I have a vague recollection of a green book cover and of a garden/nature being important in some way.
Any suggestions will be very gratefully received.