The closest parallel to her current experience I had in my own life was my sophomore year in HS, when I had a number of friends 2+ years older (some were on what was jokingly called "the five-year plan" at our then 3-year HS). And one thing I can tell you is that, though these older friends were awesome in that they were very accepting of me and never treated me as a little kid, I could never shake the feeling that they were superior to me because they were older, because they were doing things that I had no experience with/was not ready for, and that I may be intruding to a certain degree.
Of course, this is where personality kicks in, because though I may have felt something like what your DD appears to be feeling, the response was very different. I love a challenge, and so my response was an I'm-going-to-keep-hanging-around-with-these-people-until-someone-tells-me-to-stop sort of thing.
Taking on any kind of leadership role among this group was pretty much a non-starter. To explore that, there had to be age peers. There was just no way to shed the subordinate feeling with older kids, even when there was no justification for it.
The biggest difference between myself and the older kids, naturally, was with their sexual relationships. I'm sure the kids in my group were FAR more promiscuous than your DD's group (5 year plan vs. AP students), but as a younger boy there was never any reason for anyone to try to insinuate me into that activity, because all the older girls were looking for older boys. Your DD's experience, as you've already seen, WILL vary. Put me in the camp who sees avoiding older kids plus trying too hard to fit into her age cohort plus dressing in burlap plus girlfriend roleplay equals your DD running fast and far from that sort of thing... a very natural reaction, IMO.
I see reasonably attractive 14yo girls getting leered at by grown men all the time, and I'm sure your DD has noticed that, too. So there's going to be a sense of vulnerability there all the time. Her behavior could be a response to that, as well.
As a male, I have no insights to share with you on how to help her overcome any of this. All I can share is my insights on where I think the problem lies.
Maybe... pepper spray?
