or, it's not only Tolkien I keep going on about
Aslan didn't do anything to Susan. She did it to herself. She doesn't return to Narnia because she doesn't believe in the place any more. Lipstick is not the cause of her (self-)banishment but a symptom of her disease. She's a teenager who wants to be all Grown-Up and Fashionable, and retaining appreciation of her childhood loves and fancies doesn't fit in with her "mature" self-image. Real maturity, as Polly says, would embrace at least a fond recollection of what one enjoyed in childhood.
(the generating irritant)