I wouldn't call her a social retard, she seemed to get along with people very well, even if she wasn't always the brightest about it. Which, is your second point, her being naive. As far as that goes, being naive isn't so much a fault as a positive for her as in Anime that's pretty much considered an attractive trait, and to begin with, it never really causes her any problems.
And I don't give a shit why Leeron did it, he still did it, and had it been someone else he would've helped them just as much. That's his problem, he allows people to use him just to put his skills into work, otherwise as another anon put it, he has to deal with being surrounded by retardation.