Concerned but don't want to give up hope

I am final year engineering student, I am in love with my first cousin for 2 years, She is orphan, she lives in one of our aunt's house from 2008 which is at 1 minutes distance from my house. There she has to do all the household and other external works by her own, her education has also stopped from then. So she has no one but me to share all her true feelings.Our family is going to fix her marraige very soon but she want to be with me. My parents and other family members are not very flexible by nature and most likely they will not accept our marraige. We don't want to hurt them but want to live together. So we will try to delay our marraige as much as possible but as we don't want to be separated from our family after they know the truth she has to be with the family members all the time and they will do their best to ruin our life. She is afraid of overcoming that situation. So how to make her ready for that situation? And for me how to do the best to bring peace in both side?