In the words of Theon: "Do you know what it's like to be told how lucky you are to be someone's prisoner? To be told how much you owe them?"
She's a 14 year old girl and his family has held her hostage for a year and killed her father and she has been psychologically abused by some prick.
What a bitch for not being able to get over that just because Tyrion was nice to her that one time, amirite?
Bullshit. The anguish was caused by that dbag, would-be king. Tyrion has never done anything but be kind to her and try to help her. Not to mention, she betrayed her family to begin with because she wanted to be with doucheking/prince. If someone comes to my rescue when I'm on the brink of mutilation and/or death, I'm grateful to them. The last time Joffrey said "my mom wants ____ alive," he cut that person's head off. Who knows what he wanted to do to her. Probably mutilate her while keeping her face in tact. I'm not saying she should go to her knees and blow Tyrion, but she should be appreciative of the things he has done in her favor. You stand up to the would-be king and you're putting your life at risk. He didn't need to do that.
I know The Hound (the other dude who saved her life) is very intimidating, so she would naturally be afraid of him, being a teenage princess and all that jazz, but it's not like Tyrion has that presence. She hates him because she's a vein bitch who only sees a worthless midget. If he was a gay knight of roses, she'd be sneaking his gauntlet in her snatch on a nightly basis.
[edit]I am drunk, so please excuse my post if it sounds a bit unhinged. ;b I hereby envoke the Baratheon sanctuary!