Mistress T doesn't like lazy ponies. She likes it when they work hard for her because it is a sign of devotion to her. Their suffering, exhaustion and endurance to carry her is a symbol of how much they worship her. Naturally she understands that there comes a point when the pony is tired and cannot continue. For this reason she likes to use her cruel spurs and her whip to get more and more out of her pony as he starts to become exhausted.
You can also check out more of Mistress T at her Mistress T Fetish Fuckery clip store.