Can my fiancé leave her mother if she is 17 and 4 months from turning 18?

Her mother has her diploma and she is also certified CMA. She doesn't need her mom and her mom is a drinker. She doesn't feel right there because of it and she thinks that it is unfit for her to stay there so can she move in to my mother’s house like she wants because it’s a better environment because no one smokes or drinks there at my mother’s. She want to live there until I get out of my mechanic training to keep herself on the right path. She has been without her mom for a year and a couple months or so. I have been trying to get an answer for her so that she can do it.