DAY 11: STRETCH
(Another bit longer episode). Maira actually had not told the whole content of the letter to Diego, nor the whole truth. The spell which turned her into a mermaid didn't rely on her father's life source (otherwise she would have turned back into a mermaid much sooner), but actually in his trident.
Her father may have died twenty years ago, but the trident itself may have been destroyed/lost only recently. Nereus had predicted something like this could happen, so he wrote the guidelines for Maira to recreate the spell: she would have to collect a special object for her from each one of the seven kingdoms of the sea. He also wrote the spell for Maira to turn her mother's seashell into a "mermaid" tracker. Maira was not a gifted magic user like her father (in fact, she didn't even like to practice magic), but it was such a simple spell that even she managed to complete it.
The spell would make the seashell glow brighter if Maira approached another mermaid or something related to them, so now Maira had at least a clue to where to go. So, even though the princess didn't find anyone in the South kingdom, she didn't lose hope. There was still something she could retrieve from there. She recalled her mother used to keep her makeup and other "trinkets" hidden somewhere in the lagoon. With some difficulty, she finally managed to stretch her arm and reach for the only object she had found, one of her mother's seashell combs." "I think this will do", she thought. . . (Only now I noticed some plot holes in my story, so I came up with this part trying to solve them. You could say I had to "stretch" things a little bit 😉) .