My ex friend wants to be friends with me again but I'm not sure. Should I be friends with her again?

We haven't spoken or seen each other in four years. I don't understand why she wants to be friends with me. She took complete advantage of me, she treated me like crap and insults me. Also she has been disrespectful. She messaged me on Facebook saying let's me friends again and she's been crying because she missed me so much and I was her only true friend. True friends don't take advantage of disrespect each other. I was a stupid fool for letting her take me for granted. I really was. I admit it. I don't know if I wanna be friends with her again. She told me she wants to be a better person. I'm not sure. Everytime she said she wants to, she's back to her old ways. No wonder a lot of people abandoned her. What should I do?