Who's got money on Maho being the Princess' descendant or reincarnation?
I don't know. Mira did a story with the same setup before (Crimson Fantasy). In that story, there definitely was some unconcluded connection with the former partner but that took the back seat to the actual romance between the MC and what would be the mermaid in this case. As in, the new romance helped her get over the old love I'd definitely prefer it if she did it like that again, this time preferably without any connection. There's probably some connection though.
Well yeah, it seems obvious that she will realize that she's made a terrible mistake and honestly loves Maho.