Perhaps the reason why there have not been any words is because there has not yet been a chance or moment to speak the right ones? The Seven Gods of Westeros do have ways that are ever mysterious.

Stammering and lit up like a beacon does make one lose sight that she is a grown maid. She feels like a child. Her straw colored hair musses as she shakes her head because the wonder can be from her size or brutishness. "You're very, very kind." Ah, true words at last they come.

Brienne steels herself with all that's in her as though this is another bear pit.