How do I unlock this character on Mario cart wii?

I went on a website and it told me how to unlock the characters on Mario cat wii, but on some of them it said, "get a one star rank on all the 50cc sups" or the 100cc,and 150cc cups. what does it mean? I got gold on all the 50cc cups already, but I didn't unlock baby daisy, which is what the website said. Is the website wrong or am i doing it wrong? If so please tell me how to unlock the characters. I have unlocked roselina, dry bones, king boo, and diddy kong.