I guess I used to be a dependent friend myself (not as much as your friend), my dependancy was because I didn't have (and I didn't search for) other friends: everytime I was going out was with the same (girl) friend of mine and when she got a boyfriend and stopped going out I did too because I didn't have anyone else to go out with. Now I see how stupid I was not trying to meet other people and have other friends, it just extinguished my social life.
Your friend must realise that she shouldn't be so dependent on you and, for her own good, she should try to meet other people, talk with other people, going out with other people...then she wouldn't be so dependent on you (that is not a healthy thing) and you wouldn't feel so suffucated.