This discussion may contain spoilers!
In season 1, Clementine was trying. She tried to be nice, and although I think she's responsible for a lot of problems (Talking to the man on the radio, trusting him, never following the group and never saying to Lee where she was. How was he bitten? Because she didn't listen.) and she also does, that's probably why she's getting thougher in season 2.
She probably feels guilty for Lee's death, she may be trying to hide her feelings by being thougher. But there's a difference between being though, and pouting.
Clementine is really annoying me. She met a lot of good people, she saw them fight for her, and she tries to help them back, to be part of the group. Maybe not frowning at every person she talk to would be a good start for people to trust and respect her. Even Walter ! Walter who was the nicest of all people we ever met, AS SOON AS she's alone with him, she starts pouting. He was only cooking and offered her to participate, exactly what she wanted : to be part of the group. And... She's rude, mean and frowning.
I try to trust people and let every character she meets have a chance to show how nice they can be... But with Clementine always, always being mean to everyone, it's really hard.