Yeah, my DD fits this mold, too, except that she's definitely not an introvert, because she craves social interaction. But put her in a new social situation, and she immediately becomes a fly on the wall, drinking it all in, before she makes up her mind to engage. Once she engages, she's very witty/silly, and a leader of the group.
How long that "fly on the wall" phase lasts is variable, depending on the situation. Sometimes she feels comfortable almost right away, and sometimes it takes a while. And sometimes she never feels comfortable in a particular group.
In our case, we noted that this is one of those personality traits that's hard-wired into her brain circuitry, because she was demonstrating this behavior at birth. DD made it perfectly clear that she didn't appreciate being placed in the arms of people she'd never met. DW and I had to make it a rule that people were not to pick her up until she signaled to them that she wanted to be.
So, like HK said, this is just who she is. Resistance is futile.
