You have no idea what rules she was/wasn’t following. She could have been disrespectful, violent, etc. Maybe she wasn’t. Either way, she’s 18 and she left the house. She can easily finish up school at a public school and get loans to go to college. She is not out of options, she is not alone, she is not homeless, nor does it seem she’s lacking the intelligence to survive on her own. Therefore, she can move on with her life without suing because she didn’t get the family she asked for.