Some babies just aren't as trusting. You aren't nervous around strangers who try to get her to smile, are you? If you are, she can sense that, so she just won't smile. She'll be able to tell if you tense up while holding her. She'll be able to feel the difference in how you hold her, in your breathing, etc.

Otherwise she just might not WANT to mile at these people. There's nothing wrong with that. I think it's good that she doesn't want to jump into just anyone's arms!

She's normal, so don't worry about her. You have a very healthy baby and I'm sure she's beautiful! Hugs, Lee