Moving out before 18

I and my girlfriend are both 17, she turns 18 in febuary. We have been together for over two years and it has always been the plan that she would move in with my family right when she turns 18 as her family consistently makes her mental health worse. We only have four months left but it seems the closer she gets to 18 the worse her family becomes. My family is supportive and ready to take her in but we know if she tried to leave before 18 they would fight it, are there any real options to get her out? Thank you, Location: washington