How do i help her out of her painful love situation?

Shes growing up. Shes gona make bad decisions. Just be ready to help her throught it when she realizes that she made the mistake of putting this boy ahead of her family and responsibilities. Be supportive and try not to fight with her. Try to stand up for her when your parents argue with her. Get closer to your sister. Get on her good side . Then when you think she relies on you and you are so close, Be gental but tell her how you feel, Tell her your scared and dont want to see her get hurt. GOOD LUCK