This is a cool theory, and evidence wise I could see it being right, but it doesn't feel like it lines up narratively.
Lift is from Rall Elorim. Book six is Lift's flashback book, so we will likely be seeing lots of Rall Elorim in the flashbacks. As well, there's a good chance her storyline in the modern portion of the book will see her returning to Rall Elorim and facing her past. If that's true, it doesn't make sense for book five to have a very significant plot about Rall Elorim and its secrets when book six will also have a plot about Rall Elorim and its secrets.