I think she was ungrateful. MANY of the America Next Top Models have gone far. I've seen SEVERAL of them in television shows, commercials, and print advertisements.
I think Tiffany had a chance to win, and in that particular challenge, she did better than everyone. She just gave up, but yet at the beginning of the season in auditions, she was making it seem like she was going to face through adversity. It didnt help that her GRANDMA turned her lights off to help her get on the show.
I think Tyra used her as a lesson to say, if you have an opportunity, don't give up just because you "think" you cant go far. Having that attitude wont get you far in life, and it will only limit your potential.