I am giving a bullshit on those theories from "GameTheory" videos. If you wish to look for the videos, they're on YouTube and you have to search them out yourself.
I mean... why does anyone immediate believe that Rosalina is Peach's daughter? Where's the completely science proof that she's Peach's daughter? I don't give a fucking about storybook - it's such to be ancient time - like to those details of Zeldas; as seen that ALBW (A Link Between Worlds) Zelda is a descendent of ALttP (A Link to the Past) Zelda, which don't meant that they're same Zelda. And no, Peach ain't a reincarnation of Rosalina's mother, who was also Peach's ancestor. I can understand that all Queens/Princesses, from old time all way to Peach's time, would be blonde, but Rosalina as Peach's daughter? Nah, toss that away.
What are Peach's blood type? Rosalina's blood type? How about Mario Brothers' blood type? Are they even confirmed and matched?
Big Bang Theory just fucked you up - it just reset the area base on YOUR time, not whole history and throw you in the past. If it did, then it should have been named "Super Mario Time Galaxy" or some shit.
Also, had Rosalina called Mario "Father" or "Uncle Mario" (if Peach married to Luigi instead), asked Mario to save her "mother" (Peach) in same fashion as Bowser Jr, but kindly and gracefully? So far, I didn't see or hear(sic) her saying those words (Father/Uncle/Mother/Bullshit) so far. That therefore proved GameTheory's bullshit "theories" backfired.
And if Galaxy 1 was cleared and Rosalina vanished when Mario/Peach/Bowser returned to their fucking world, then Galaxy 2 won't happening, as she ceased to existing and never come to help them anymore - it's because she is coming from the "Bad Future" (Yeah, color me surprise, you bitch!) and if that "Bad Future" ceased to existing, so is Rosalina. But that ain't happening, Rosalina still coming and Galaxy 2 is still activating.
That therefore the whole theories GameTheory had made and posted on their fucking account is just whole waste of the research, waste of space and waste of the talk/time. Rosalina is neither related to Peach or Mario brothers.
Also, ignored Daisy, huh? If someone spoke about the ear lobes, Daisy also possess that trait, and you ignored her? Is that because she's fucking Fan-made character and is fucking Sport player? C'mon, put up your balls and think careful! And also, Baby Rosalina is NOT Rosalina's looks, because that character is fan-made and just chibi looklike, and in the storybook; Rosalina's hair was peach orange before she grew old, became into present Rosalina we saw.
In long story short - GameTheory is wrong, Rosalina is not related to Mario/Luigi/Peach, let alone being Peach's ancestor's daughter (I would be wrong with this one, but I don't care - it's just pointless theory of mine, which I can easy dismissing if it's fake).