Wells has been having some touch and go with contracts and publishers. My guess is that she expected it to be just a trilogy but then the series was popular enough that she was able to publish some more. But she says that Harbors of the Sun is the end of it. I attended her Kaffeeklatsch at Sasquan, and it was great to hear her talk about the series and her other books. She's criminally neglected as a writer, IMO.
Have you seen the various bits and pieces she has on her site? And also, supporters on Patreon get to see all sorts of chopped scenes and so on.