You can see Meme with her father back in Ariadne during the most newest chapters of the raws - chapters 124 and 125.
For some reason apparently Barbaros needs both his daughters with him in order to use the full extent of his powers. This explains why he wants both Leana and her sister.
I can sadly confirm that this does involve time travel. Leana is Pipi from 10 years in the future, or at least has memories of that due to time line shenanigans.
Pretty heavily unsold me on catching up with this manga. I really hate time travel.