From Final Fantasy Wiki

Ester is a minor character in Final Fantasy VII. She is the best manager for Chocobo riders in Gold Saucer's Chocobo Square. After overhearing a conversation between Cloud and his party with Mr. Coates in the Corel Prison, she agrees to help Cloud out by teaching him about Chocobo Racing. Ester gives Cloud a Chocobo for the race. If the player fails, she will keep on giving better and better Chocobos until they win. After Cloud wins the race, Ester can be found again at the Chocobo Square. Talking to her allows the player to register one of their own Chocobos in a race and ride them.