Oh, of course. Luckily for Yvaine, Tristran does have a sister.

"One," he replies, helping her down the step -- crutch and all -- and to the outside grounds. There is a soft breeze that floats past them, clearly smelling and feeling of spring.

"Her name is Louisa." It is through her that he met Victoria, after all. But he isn't going to say that aloud.