YA/Teen Book Series - 1st Book has a black cover with a neon green wolf or animal printed on it. Main character is a young girl, and she crosses some sort of hedge and enters a different, magic type world.

That's all I can remember from it, I only ever read the first book but I know it's part of a series, possibly at least 5 books. I read this as a kid and really liked it but I cannot for the life of me remember the title or the author.