My gf is living in joint family.we both love her much.bt the problem is...PLZ HELP GUYZ N GIRLZ...Q IS--------?

We both are studying nw and her grandfather will decide her life partner.grandf is very hard and strong person. I just marry with my gf.and she is not want to leave her family and me.i just want to marry with her...bt how can i explain her grandf??? her family is orthodox bt she is educated and she dont want to go against her family. we r in same religeous.