User blog comment:Roranoa Drake II/Chapter 825: Too Short, but Golden/@comment-137.175.139.190-20160508235204/@comment-24850639-20160511150948

The simple answer is we have no idea. We know nothing about her whatsoever, so a dream, or what she potentially offers to the crew are things that are complete speculation right now. We need her backstory before we start to take stabs at these things.

On the same note however, I do think that Big Mom's daughters are a mixture of biological vs. adopted/kidnapped. By having these women swear their loyalty to her as their "mom", Big Mom can then use them to arrange political marriages with whatever faction or country she likes.