I think she may have same kind of power like the MC and other characters except her/his power can make her/him attractive to others , I mean whan Mia ask you who of the girls to you like if you choose Demi she will say "another victim fall for her charm" or something like that but the point is there was many people falling for her, which could mean that she have power like a succubas or maybe she is just charming and we are thinking to much
I don't think that Demi could be 'infected' because they can sense each other (with the exception of what's-his-nuts because he messes with the mind). She(?) also appears to have trouble with all of the people attracted to her(?) while all of the 'infected' can control their abilities quite well. I think that it is an innate ability.
What I meant is that she literally get along with any one even the Dean , the teacher and the rich boy (can't remember his name) but there a part were Demi was taking with him and then other people started appearing and fighting over Demi and when she run away she said to herself "did I overuse it" I think she was taking about her power the power that makes people love her and not to forget about the MC Hero identity fan club ( I named him DARK ) the club have a huge number of fans I bet most of them are here for Demi