People like that are capable of being whomever they need to be, depending upon their audience and the circumstance. A person can woo you with sweetness and the appearance of friendship, then backbite you with no mercy. He or she can do this to peers, significant others, parents, siblings, those weaker than they, etc. etc. etc. Females around high-school age in particular are great at this kind of behavior. If a guy she has her eye on wants a funny girl, she'll be funny. If he wants a tough, independent girl, she'll be that. She'll mold herself to whatever shape will enable her to uncover his weaknesses, then she'll exploit them, and he may or may not see it in time to extricate himself unscathed from the relationship. So, to answer your question, what draws people to her is whatever they want. She'll make herself whatever is attractive to them, and be that until she has them where she wants them.
Note: I know this, but I was not one of those girls. I knew lots of them, but I wasn't one of them. Just thought I might put in that little disclaimer.