I have noticed this as well! I have a bit of a theory that could be wrong, but is food for thought.
It’s no secret Carol’s life before the ZA was a nightmare in itself. She lived in constant fear of her husband’s tyranny, never knowing what might set Ed off that day. She was physically beaten to the point of needing medical attention at least twice before. She had to watch out for Sophia at all times, protecting her from her own father’s wrath as well as his inappropriate gaze.
In a sense, she was much like the individuals we see alone or in pairs in the ZA. They’re wandering around, constantly on their guard. They are often doing without basic essentials, making do with what little they have. They’re very tired and haggard from having so little support, wandering around in a world full of people they feel as though they can’t trust. Carol was a one-woman army in a never-ending battle against the man who isolated her, made her live in fear, constantly looking over her shoulder while keeping her daughter near.
Now that Ed is gone, Carol has had the opportunity to blossom into her own woman. She has always contributed to the group with what skills she already knew (sewing, laundry, cooking), but then for the first time, she was able to explore other areas where she could help out. She learned she was a decent shot when she learned to shoot a gun. She learned she was a rather good nurse under tutelage of Hershel. She could finally be more than just a housewife and mother.
Best of all, though, she was no longer alone in her fight for survival. The group shares a common enemy with the walkers, and they all help one another so that no one struggles alone. Carol can finally find some peace knowing that even though the world she lives in now is no less dangerous than living with Ed, she is no longer alone.
Daryl… that’s a bit more complicated. I’m actually a bit hesitant to speculate, but my best guess would be that he has grown up a lot over the last four seasons. He has taken on a lot more responsibility as one of the main security personnel, the hunter of game, one of the leaders of supply gathering parties, and a member of the council. He’s often shown as the first one to offer to take on dirty jobs (grave digging, emergency runs) that no one else wants to do.
Sometimes I think in his eagerness to do these things has taken its toll on him. Why he spreads himself so thin is a question I’ve pondered for a while. Is he still trying to prove his worth, as he constantly had to prove himself to Merle? Is he trying to atone for his past “sins” against the group, such as the initial plan to take over the Atlanta group? Or is he trying to make up for a lifetime of following Merle when he could have done something with his life?
I’m sure other folks out there have much better theories, but those are my personal rambling thoughts. ^_^