So I was looking at the Pure Good wiki on FANDOM just for fun when I saw on the movie version of Rosalina’s profile that she and Peach have unnamed birth parents. I don’t know if it was hinted at in the film they had birth parents but if this is true then it could be a clue for what comes next in the third film.
Peach: so it’s true. We….
Rosalina: yes.
Peach: (starts tearing up) did you…really…
Rosalina: (starts tearing up too) Every day.
(Flashbacks play of peaches days in the mushroom kingdom from catching her first fish, to the training course, to the day she became princess. Each of them reveal Rosalina was always watching her everyday like a sister would.)
(The two share a hug together in tears.)
Rosalina: I knew I would see you again.
Peach: and I knew I would find you.
(Mario and Luigi watch in the background and smile)