L.S.
perfectly normal. When my baby approaches someone new or familiar he won't smile for a while or waits until I smile. But he warms up eventually, especially if I continue smiling and acting like a really like the person. They will take cues from your body language and how you react to someone. So don't worry about it. If your baby doesn't make eye contact with you (but it sounds like she does) than that is another matter all together that you can bring up with your pediatrician, but if everything is alright at home, then it is just stranger anxiety.