How does this sweet little baby turn into .......

...this overnight?
Most days she is a drooling, slobbery mess with food in her hair, but i love her a lot. Boy does she have an attitude though and i have been setting myself up for this and she knows it. Usually as soon as she cries or whines i gave her whatever she wanted to get her to stop. It is coming back to haunt me now. She is not even 1 and she already has tantrums. As of the other day i am starting to work on this some and not give into her every whine, which makes her throw a tantrum and sit on the floor and cry if she doesn't get her way. Eventually she gets over it and will start playing. If i turn away from her and ignore her she crawls so she is sitting in front of me and i can see her crying. Usually this only happens when she is really tired. I want to end it right now before she gets into the habit of it. I see those wild kids on Supernanny and hope she never gets like that.