You win baby daisy on the 50cc not on a specific cup you have to gain star ranking for Mushroom, Flower, Star, and Special Cups
Win 150CC special cup
You have to win first place on 150cc Special Cup
In Mario Kart you have to do the 100cc challenge and win the special cup (Edit) Well that is how you unlock Daisy not baby Daisy.
Win 50cc Star Cup
win in 1st or 2nd in the cup
Get the Gold cup in all 50cc , 100cc and 150cc cups
no
You have to win the 150cc special cup to unlock Daisy
Just win good trophies in enough races first, and it should unlock characters and the cups!
on 150cc, you should win princess daisy
Baby Daisy
You must win the Special Cup in 1st place under 100cc and then it should have your Mii in the character selection area.