S.Z.
It's actually very normal for kids to become more timid and unsure as they get older. Very small children have a limited idea of what kind of "bad things" might happen to them. The worst thing they can imagine is usually something that happened to them - another child taking away a toy - or fear of being separated from Mom and Dad. When they get older, a whole new range of fears is possible. What if other kids don't like me? What if they make fun of my clothes? What if I spill something and everyone laughs? Add that to the anxiety they sense and hear from adults every day, and the world can be scary. What does "economic downturn" mean? What if we have to move? What if there's no presents at Christmas? Then there's the loud adult voices arguing about war, health care reform, elected officials and other things they don't understand. Then there's the things they, unfortunately, DO understand - shootings at Fort Hood, a serial killer in Ohio, missing children (including a 5 year old whose mother was just charged with human trafficking and child prostitution!) Being cautious seems like the safest thing to be.
All this means that you need to spend MORE time pointing out the good in the world and in her life. Be very, loudly and outwardly grateful for family, food, jobs, clothes, a place to live, and don't add any "buts" on the end (as in, "I like my job, but..." or, "I love Grandma, but...") Praise her, realistically, when she masters new skills. When you have to talk about things like "stranger danger," emphasize that she has the skills and ability to keep herself safe. At the same time, tell her that people who have bad things happen to them don't deserve it. She's too young to truly comprehend the idea of random violence; telling her things like, "Noone can really prevent these things," or, "It could happen to anyone," will make her feel very unsafe and unsure.
Also be aware that if you put too much emphasis on changing her thoughts or behavior she'll think, "What's wrong with me?" or decide that you'll only love her if she behaves a certain way. Make sure she knows that real love is unconditional, and there's nothing "wrong" with her.
I'm not sure if this helps, but hang in there! :) All things pass in time.