Believe it or not, when toddlers show apprehension about the world around them, it's actually a healthy sign. It means she's aware of the dangers out there and wants to be cautious. This is a good thing. It means your toddler can determine the difference between the people she knows and strangers, and she’s wary of unfamiliar faces. It may also be a sign that she's explored fearlessly and suffered the consequences (like touching a hot stove and burning herself).
Becoming more aware of surroundings — what's safe and what isn't safe — is all part of the learning process. But, in time, she'll feel more confident and in control when it comes to new experiences.