I might categorize this as a historical romance, except that there's more than one -- through no fault of her own our main character is a serial monogamist. But it's more of a saga, spanning Macha Sheridan's life from roughly age 14 to 40 in Ireland and England, starting in 1895. Her rise from a near-penniless orphan cast out of her Traveller camp for defying custom to the circles of nobility is not without scads of heartbreak, but well worth the time spent reading it.
I actually stayed up all night reading this book, which I miraculously found at a garage sale just a few weeks after seeing it recommended on a horse book blog as a good example of horsey novels aimed at adults. Although it took me years to actually open it, I now heartily endorse that rec. Horses are the one constant and central fixture in her life, as both companions and a livelihood. Although she can be ruthless as a trader, even laming horses in a second foot to make them appear sound, there are a few special horses she cherishes through the rest of their lives and won't part with no matter the circumstances. I grew very fond of these horses.
I didn't think I could possibly enjoy it as much after her departure from the open fields of beautiful Ireland, but I was quickly riveted by her navigation through Edwardian society, funded in part by her uncanny ability to judge horseflesh well enough to pick race winners with near perfect accuracy. In her personal life, the highs and lows here are even more intense than before. By the time I finally shut the book, I was exhausted in the best possible way, feeling like I'd lived half a lifetime and watched the world change right alongside her.