Paint the Wind by Pam Munoz Ryan
Orphaned early, Maya is one of those poor little rich girls who have almost everything they need except love. Only childhood pictures of her father are permitted. All Maya has left of her mother is a box full of plastic horses and one photo rescued from her grandmother's effort to destroy all traces of her mother and father's life together. But when a stroke claims her grandmother, Maya discovers her mother's family not only isn't a batch of illiterate pig farmers, but actually wants her. In Wyoming she has aunts, uncles, and even a cousin - and there are horses!On a one to ten scale? I'd probably give it a 6 or so. It wouldn't stand up to the challenge of Firehorse, Serilda's Star, or the Bonnie books by Pat Johnson, but horse-crazy kids devour pretty much anything featuring a high mane & hoof quotient, and this one will fill the something-new bill nicely.
Rather better than I expected after a slightly sappy opening. The parts featuring Maya are very readable. The parts featuring Artemisia (the mare) are a bit over the top. The behavior described may be horse behavior, but it's too anthropomorphic for my taste - might be right up the alley of a ten-year-old, though. And Maya's ultimately a likeable, understandable young heroine.