Any recommendations for books about girls and horses for bedtime reading (mostly me doing the reading) with my six year old daughter?

DD1 and I just finished reading "Me and Katie (The Pest)" by Ann M. Martin (yes, the author of the Babysitter's Club books), and the poor girl cried her eyes out when it was over and I had to tell her there wasn't another book in a series about the characters. Seriously, I cannot tell you how heartbroken she is. It's adorable, but sad at the same time! So....I'm looking for some other books she might love as much.

I remember a series called "The Saddle Club" from when I was young, but it appears the books are out of print and our library doesn't have them. We've already exhausted the horse-themed books in the "Babysitter's Little Sister" series by the same author.

Thanks for your ideas!!!