Snow Whites baby, Streak was tiny. One of the other ducklings (a little older and larger) took to her and stayed by her side. I left her with the ducklings and Snow White and Mommy and all was well. Eventually she caught up in size and I have to stop and really look to tell which one she is. I have 3 that look very similar.
So, I vote to leave her with the Ducklings. As long as they are not picking on her, she's fine. Looks like Dotty and her are friends, Dotty should keep her warm when needed and keep the others away from her. Amazing how they do that, when they are so young.
Besides there is the issue of them not accepting her back when she is older, that is a bigger concern. You don't want her to grow up thinking she's a chicken.