What if Cinderella has more than 2 step-sisters, as is traditionally told? Maybe she had a 3rd, beautiful step-sis, Anna, who ran away to WL with the knave?
I posted something similar a little while back. Who’s to say how many sisters there really were.
If Ella’s step mother and sisters really were horrible, then maybe Ana got outta there as soon as she was able. She used Will to escape that life, and then she used the King to escape her life with Will.