Books by Monica Dickens or Christine Pullein-Thompson are about real ponies and much better than all this Fairy Pony rubbish. Although they're probably a bit dated.
A really good encyclopedia - I had one given to me at age 9/10 and I still use it now, nearly 30 years later. Don't worry if it seems too grown up - she can start with reading about evolution & different breeds & sports and get onto the the veterinary stuff later in life!
DVD of Pony Club Games.
There are lots of toy horse things around of various sizes - Early Learning have some which aren't bad, there is a very good make that most tack shops stock but the name has gone out of my head! Begins with a B...?!?
Or try this site for childrens clothing etc RideAway - the site is a bit crap but it works and delivery is quick.