They are, however, allowed to change, only it must be a complete change.

At present she was full of jealousy of Wendy.
What she said in her lovely tinkle Wendy could not of course understand, and I believe some of it was bad words, but it sounded kind, and she flew back and forward, plainly meaning "Follow me, and all will be well." What else could poor Wendy do?
She called to Peter and John and Michael, and got only mocking echoes in reply.

She did not yet know that Tink hated her with the fierce hatred of a very woman.

And so, bewildered, and now staggering in her flight, she followed Tink to her doom..