How do i make a person realize her negetivity?

Hey guys need some help here. i got a fren hu is very helpfull n sweet......infact she is liked by everyone in our frens cirle. but shes very firm wit her principles. in some ways its ok but some of them r not at all helpfull 4 her, she doesnt even realize tat being like tat is actually not doin any good. infact it gets more complicated. how do we make her realize this?she is queit stubborn about this.