Besides having one-in-a-million looks (speaking as a photographer), her expression, tone, and manner conveyed that she was genuinely happy (not overly earnest, nor fake, nor pushy, nor airheaded/high) to be representing some charity, and she instantly liked us, and thought we might want to hear about this charity. (I did manage to keep my money, but I had a lot of practice dodging those street teams.)
After we walked away, the social scientist (also a woman) said, matter-of-factly, "No one has ever said an unkind word to her." I could imagine that being literally true.
I've met a number of very charismatic people, but they usually seem to have some awareness of it. I'm thinking maybe one of the higher tiers of charisma effect might be when the person doesn't know (or doesn't seem to know) how charismatic they are. Maybe they give the impression of seeing the world and others through a more appealing lens, and people respond well to that.