Rosalina

I don't now how you get her but i have her to. she only came in the game and i do not now what i did to get her.

According to other sites you need a Mario Galaxy save then complete a series of Grand Prix Cups (i.e. either all 50cc, 100cc or 150cc Cups). And if you don't have a Mario Galaxy save then you need at least 1 star rank for all Mirror Retro Grand Prix Cups.

well that is very weird I have not even done a single 100cc
cup but is till have her.

I got her but dont know how, i do have a save file of Mario Galaxy.

Might have been after I completed all of 100cc...but im just guessing.

What's the method to unlock her if you don't have a SMG save file?

quote Gamespot.com Walkthrough

-------------------------------
Unlockable Characters and Karts
-------------------------------

General Unlockables -
- Completing the first two cups in each type will unlock the third; completing
  the third will unlock the forth.
- Getting trophies on all of 50CC and 100CC will unlock the ability to
  race with both Karts and Bikes.
- Getting all trophies in a class displays credits, and congratulations
  screen (with your Mii!) that you can post on your Wii Message Board.

Remember, you need to get a GOLD trophy to unlock whatever you need!

50CC
----
Mushroom Cup  - N/A
Flower Cup    - N/A
Star Cup      - King Boo (character)
Special Cup   - Piranha Prowler (L kart)
Shell Cup     - N/A
Banana Cup    - N/A
Leaf Cup      - Turbo Blooper (M kart)
Lightning Cup - Diddy Kong (character)


100CC 
-----
Mushroom Cup  - N/A
Flower Cup    - N/A
Star Cup      - Twinkle Star (L bike)
Special Cup   - Mii Outfit A (character)
SHELL CUP     - ROSALINA (CHARACTER)
Banana Cup    - N/A
Leaf Cup      - Dry Bones (character)
Lightning Cup - Rapide (M bike)

maybe you get her on 100cc shell cup if you dont have a SMG save file i don't now really.