Margaery laughed at Loras' turtle comment, she didn't think her brother would be happy with a slower pace. In her dreams he was the Knight of Flowers, the best of the best and he was always coiled and ready for action, not unlike he was here really. She knew this was a way of trying to fill the space left by Renly, even in her dreams he had only swallowed his grief because she had needed him to protect and support her in her ambition to become Queen.
Here she wanted to protect and support him in return but she wouldn't push. At least not yet.
She returned his smile and nodded; when they started going faster she'd hold on. She was rather looking forward to it.