What can i tell her, to help her undertsand!?

Sounds as though she may not want you their. If she was cared for you, she would support your decisions, let her know I will support my daughter, and I will be in her life, trust me. If she want to be with you, she will be their to back you, and support you! If she will not agree with your decision, that means she is not in your corner, so you need not waste any more time on her!