D.D.
I have one cautious kid and one no-fear kid. The cautious one has always been that way. He walked at 14 months and was slower to learn to swim and ride a bike. But he also takes time to think things through and coaches love him because he will take the time to learn how to do things the right way. IMO in many ways he's easier to parent than a no-fear kid.
So yes it may be personality and if so, there are many great things that go with this personality type.
If you are worried that is more than this - if she's not making eye contact with you when you say her name or other things, then by all means call early intervention for an evaluation.