I love books. I used to have a pony named Doodles (best pony EVER) and I once found an book (1977, not old) about a pony named "Doodlebug" at a flea market.
It looks like your book has nice illustrations. My "Doodlebug" book has nice ones, but the pony does not look a thing like my Doodles did, but instead looks a lot like Peanut!
I found a fairly old copy of Black Beauty at the same place a year or so later.
I hope "Dapples" had a nice ending, not sad.