Quiet baby

My baby is so quiet. She makes some cooing noises and squeals at times ( with joy) she will giggle when tickled and she laughs at her sister and parents. She kinda babbles to herself sometimes. I just feel that she is a quiet baby and she doesn’t really try and copy me even if she watches me carefully. She doesn’t smile at strangers however hard they try!l but everyone comments on how quiet/ good she is. I do worry that she is developmentally behind at just under 7 months. She is an active child so I do wonder if that’s her ‘thing!’ Rather than chatting.