It does not make sense to me.
So should I just let her be? Is she missing out without knowing it herself? Is this behavior holding her back and reaching her potential? Is it going to get worse if I don't intervene?
It makes perfect sense to me. If you know all the rules for the context, and are confident you can perform in the confines of the role as specified... that's easy.
I'd say there's nothing to worry about, and she probably isn't missing out versus her own perception of her needs. Luckily, we grow up to be great facilitators, sensitive and respected managers, great friends (to the few who are let in), etc. It's a different potential.
If you want to help along the path, things I would've found helpful:
1) Go people watching with her, like at a mall or a park. Discuss the people you are observing, speculate on what they are thinking, etc.
2) A big epiphany was realizing that despite being social and talking and interacting, other people may also be observant; i.e. she could work on exposing small emotes even from the sidelines to indicate she is aware/following/understanding... A slight nod, a head tilt, glancing up in thought, a sub-vocal huh.
3) Make sure she has enough opportunities to interact with strangers in defined contexts, e.g. ordering at a restaurant, talking to a librarian, etc.
4) Explain about extraverts/introverts and that some extraverts have to "think" out loud. And that extraverts imagine introverts must be lonely and are usually trying to be helpful when they invade.
5) And never have the "what's the worse thing that can happen?" discussion when dealing with potential embarassment.
...and I've got an extravert DS7 who walks right into a store and tells the employee exactly what we are looking for and why we want it, etc. while I'm the deer in the headlights... not sure which is trickier the introvert parent with extravert kid or vice versa...
