My girlfriend loves me but not ready to marry me?

My girlfriend knows i love her very much and i want to marry her and my love is true for her. But after knowing all the things she is not ready to marry me.She is Saying "If i will marry you.My father will kill we both".I said "Ok my parents are ready to accept you.Just run away from home". She replied "It makes my family very Shameful ".Her father & brother belongs to underworld but i am ready to fight with them.I love her and I will do anything for her.How to maintain my relationship with her.Please help me....