[Jepardy]

These books were published in the 1980's-1990's. They were all children's / young adult chapter books. None of them were too long, about 200 pages max I would guess. A detailed description of each book follows:

1. The first lines of the book were "I remember the first night I went to sleep with grass and dirt(or twigs, leaves, etc) between my toes." It goes on to be about a little girl named Zoe, she is about 8 years old I believe. Her mother dropped her off with her grandparents to be raised by them. She finds a ghost named Zoey (The names could be reversed). They become friends and the girls learn that if the alive one walks down the backstair case in her grandma's house she goes back in time to Zoeys time, and there she is the ghost. In the end the alive girl helps save the ghost girl from ever dying in the first place. I believe there was something about 'stairs' in the title, but not sure.

2. Its about a girl and her mom, I think there might be more family but not positive, who move in to a mansion house. The girl is a teen named Nina Tanleven (may be spelled wrong), who is called Nine, from Nine-ten-elven. A play on her name. The premise of the book is about a painting that I think the girl travels to a ghost world, or a ghost comes out of. I don't remember much more.

3. Its about a little girl (I'd say 7-10) who moves in to a new house and finds a ghost girl living there. One of the two I believe is named Heather. The ghost died in a fire that she accidentally caused. She was a very bratty girl in life and in death. I believe there is something to do with a locket as well. The alive girl ends up getting help from her older sister/step-sister, etc. And the ghost girl is put to rest.

[eljayhalflife]

Bruce Coville wrote the Nina Tanleven series (several books)
Pam Conrad wrote Stonewords: A Ghost Story, published 1990
Mary Downing Hahn wrote Wait till Helen Comes: A Ghost Story, published 1986

Did Yahoo search, and descriptions of these stories fit your description.