Ariel throws her body in the line of her father's trident to save ursula, right? She will sacrifice herself on the behalf of some one who has hitherto, in the plot, been seen as irredeemable. I mean, i think cruel was done to ursula, and it made her cruel. And i believe that ursula could actually be redeemed, and that all it really takes is one person in an act of tremendous bravery and kindness.