Ella arouses Richard’s sensations (1.2.23) and makes him "hunger for […] sharp, frightening, breathtaking, almost painful excitement" (1.2.37). Pretty racy for a girl who just tells Richard fairy tales.
Richard’s mom isn’t really the warm and squishy type, so Richard is already old enough to go to elementary school before Ella tells him his first fairy tale. It changes his life: "My sense of life deepened and the feel of things was different, somehow… My imagination blazed" (1.2.23).
Even though Ella introduces Richard to his lifelong quest, we barely know anything about Ella (see Ella's "Character Analysis" for what we do know). Richard doesn’t even mention her after she gets kicked out of the house, because all Richard cares about is how people affect him. Ella gave him the gift of literature, and that’s all that is important for us to know.