Is 210 pounds too heavy to go horseback riding?

She weighs too much for a pony of that size. If she wanted to ride, she could lease ( or if she doesn't know how to ride) or take lessons on a horse that is about 16hh or larger. It would put less stress on the horse's back if it was larger. Just tell her gently, so it doesn't hurt her feelings! Just tell her the truth! The Morgan might be able to hold her for a little while, but I wouldn't want to take the risk of her hurting the horse's back.