To answer your first question, my friend, people in the family who I'm close to and are aware that I'm a hebephile probably would not complain about me talking to an AG in a public situation, especially if I was talking to her with three other people at the same time, which I was. Some of them do make sarcastic jokes about my attraction base on occasion, but I don't think any of them believe I'm some sort of threat to AGs. They know me well enough not to think that, but I have no idea what they may or may not say behind my back at times. However, since I am concerned that family members of mine who are family via marriage to true blood relatives who do not know me very well, and friends of family who know me even less, might get alarmed if they knew I was a hebephile (and I am unaware of how many of those particular people know) and saw me getting 'overly friendly' with an AG; you never know which of them may possibly be a hardcore anti. And of course, I would never try to talk to the girl someplace where we were alone.
As for my likelihood of ever seeing D again, it's unfortunately not very likely. She is a friend of my 18-year-old cousin, and I usually only see him on holidays and special occasions (like his graduation), and it's only during the summer that we have parties of this nature, where many friends of relatives are invited in addition to our relatives themselves. I am not sure how long my cousin has been friends with her, but I have never seen her before.
Yes, it is a shame I couldn't ask her to exchange numbers and maybe eventually ask her out after I got to know her better, and if it turned out she had that type of interest in me also. Then again, if she is not into older guys, I wouldn't want to risk creeping her out by asking her. Due to the type of society we live in today, with its rampant age segregation and its heavily biased media, she may be one of the many girls who are indoctrinated with the belief that any guy my age who shows any degree of beyond casual interest in girls under 18 are a dangerous threat to their well-being. It would break my heart if that happened with an AG I admired, since I am the type of guy who finds it very hurtful if I inadvertently creep out any girl or woman I am interested in by showing an interest in them.
As for the second girl at the doctor's office, I have no doubt too that you would have liked her had you seen her. I am not exaggerating when I say that Aphrodite herself would suffer pangs of jealousy if she ever saw that girl. That's how beautiful she was; no hyperbole in the least from me on that score.