I think she's deflecting alot of her own guilt onto Rick. She's the reason Shane tried to take Rick out. She knows she's the reason. It's just easier for her to be pissed at Rick, who actually took care of business himself, than to deal with the fact that this all really comes down to her.
And as for Carl..... come on, guys. If any of your fathers blurted out that he had killed his best friend, who was really like a second father to you, as well as probably being a pretty good guy before the world ended, I think we'd all be pretty upset by that. It doesn't mean he loved Shane more. It just means that it's upsetting.
