So Game Theory is doing a two-parter on Rosalina:
They are basically trying to figure out more about who she is.
In this video, they come to the conclusion that Peach is Rosalina's mother.
While I appreciate the video, I think that theory is false, and I have many conclusive points on the matter. Typing my response right now, I'll paste it here when I'm done.
EDIT: My response:
"Good attempt, but as a huge fan of Rosalina (my personal favourite Nintendo character), there are a few problems with claiming Peach is Rosalina's mother. It simply cannot work:
1) Interviews with the game's creators have revealed that Rosalina was, at some point in development, going to be related to Peach, but the idea was scrapped. Her prototype design even bears much more resemblance to Peach, with a similarly regal dress. No matter what you think, you can't really argue with the word of the creators, they claim the two are not related in the final game. But even without that...
2) Rosalina IS ambidextrous. One of your own pieces of footage backs it up - the 120 star ending of Super Mario Galaxy shows her holding it in her right hand, and even using it to get the Comet Observatory moving. The scene before Bowser's Galaxy Generator also depicts her doing the exact same thing with her right hand, again. However, in Smash Bros, she uses it in her left hand during combat, to control Luma and even directly attacking foes. These two points, combined with what you presented in this video, prove she is ambidextrous, since she can perform taxing actions with both hands. I made a post about this on tumblr one time, funnily enough:
http://sonicbrawler182.tumblr.com/post/93065941662/fun-rosalina-tidbit
So basically, the entire point about genetics making her left handed goes out the window. There is no "right hand bias" going on here, she can use both hands to wield her wand and do amazing things with it.
3) Rosalina also has a brother, mentioned in the storybook, in Chapter 7. To prove Mario and Peach gave birth to Rosalina, you must also prove they gave birth to a son, and that said son is Rosalina's brother.
4) Rosalina was traumatised to the point of believing she could find her mother, whom she knew was buried under a tree, in the outer reaches of space. Her family's death is something that never left her, as her bio for Super Mario Galaxy implies. Although she is monotone, she is still sentimental. If she met her mother and father, she would probably break down. Furthermore, she's a goddess. The "mother, watcher and protector of the cosmos". There are implications that she is all-seeing and all-knowing. I'm sure she would have found her parents if they are still alive.
5) The tree near Peach's Castle that you claim is the same as the one in Rosalina's Storybook looks nothing like the one in the Storybook. The one you say is the same looks like a normal, deciduous tree. The one in the Storybook looks like a coniferous tree (a Christmas tree, even).
So where is this tree where her mother is buried? Well, Gateway Galaxy is covered in coniferous trees, as well as the same flower patterns from the storybook. Rosalina visits her old home every 100 years. And in the 120 Star ending, we see her do exactly that, and in the Red Star mission, Rosalina outright calls this place her home.
It's possible that Rosalina's home was once a part of the Mushroom Kingdom in a different universe (Rosalina has tended to the process of rebooting the universe multiple times - again, space goddess for the win). However, Peach ain't her mother, nor is Mario her father. Rosalina has no relation to any of the Classic Mario characters, and her family's identity remains a mystery.
Not to mention that the various ship teases of RosalinaxLuigi in the game would be really creepy then, since Mario being Rosalina's father would mean Rosalina's uncle has a crush on her. :S
So yeah, I think your follow-up video needs to correct this video. I hope MatPat reads this and mentions these things in the next episode."
