Her Last Race by Kim Schaumburg

A successful horse trainer, a notorious hardass, who chose career over motherhood twenty years earlier; the daughter she abandoned, now a jockey, struggling to succeed in a brutal, male-dominated sport; and the rogue filly who tests both their skills.

Here's an Excerpt: Nikki slammed down the phone and lay on her bed. The anger that fueled her ambitions flickered to life and she pounded her fist against the mattress, vowing her relatives would need some real strong onions to ever make her cry. The last time her Aunt Monica had called, about four years back, Nikki had gotten so mad, she'd kicked the bed frame and broken a toe. She had won three races the next day. At the moment, Nikki felt an urge to practice her whipping on the side of the bed. She rose as far as a sitting position, then lost the urge and strained hard to recall her early childhood with Rachel and compile a list of bad memories versus good, in hopes the bad might this once prevail and kill what little expectation of a happy reunion yet remained in her heart. Nikki no longer wanted a mother for the sake of being mothered. She'd been without one so long that even imagining such a thing seemed laughable. It was a matter of proving her own worth. A matter of allocating blame.