How to unlock birdo on Mario Kart wii?

It is Easy as can be. All you have to do is set a time on time trials on sixteen out of the 32 coarses, or set a time on all of the corses at the begining of the game (since there is 16 at the start of the game) or if you have all of the coarses unlocked and don't have a time set for any coarse yet, set a time on all the coarses so you can unlock both Birdo and Toadette.