Young adult book about time travel

In the 1990s I read a book where a young teen girl would time-travel to different times/back into the bodies of other people to do stuff to prevent horrible things from happening. She time-travelled/became other people by way of a horse: it previously belonged to a lord but he treated it horribly and it died but its spirit lived on.
The book may have been written in the 1980s.
It was a series and the book I read wasn't the first. I remember at one stage she travels into the body of a girl preparing for a disco and she looked at the eye-shadow and it was lizard green with silver flecks.

ETA: This is Monica Dickens' "The Messenger" series.
I was going to say this sounds like A Swiftly Tilting Planet by Madeleine L'engle, though the premise in that is a boy and a unicorn, not a girl and a horse, and I don't think there's lizard green eye shadow and discos involved....

Edited at 2017-02-14 23:01 (UTC)
Hmm. It's not L'Engle but I do think it was set in Britain, and the Author is British? And there was something about a moor.
I think it's The Messenger series by Monica Dickens - The Messenger, Ballad of Favour, Cry of a Seagull and
The Haunting of Bellamy 4. I only read the first 2 but I remember the eyeshadow.