Think about it! She has survived where no other animal (and most people!) would survive. She escaped the trollocs at winter night, and then just happened to show up at the inn later. Without her Eggy wouldn't have went along, who knows how different the pattern would be!
She saved major characters lives numerous times, she is always there when you least expect, and most need her. Saving Eggy in that river, being there to save Suian in her get away from Tar Valon and carrying her to Salidar. Always there, and always able to escape certain doom almost miraculously.
ok, ok, even if you don't believe her ta'veren, then at least you have to admit she is a key character in the series *g*