18-year-old stepdaughter refuses to accept younger stepdaughter and 39-year-old stepmother, stepmother tells her to move out: 'I told her that if she hates us so much then she can leave'

At 18, you are an adult in every sense of the word. Sure, your frontal lobe hasn't fully developed, and you're going to make a whole lot of bad choices over the next seven or so years, but the difference between 17 and 18 is that you're going to be solely responsible—and accountable—for those decisions. That means the way you engage your personal relationships and the decisions you make for your future are on you, despite your relative inability to properly rationalize them and your lack of experience in making them.

If you're fortunate and privileged, you'll still have the support of parents, guardians, and other mentors who push you in the right direction. If you're even more fortunate, you get to spend these years in a structured simulation environment called "college," where you get to engage with other frontal-lobe-ly challenged "adults" where you can go on adventures and make all kinds of terrible decisions that you'll look fondly on and/or regret for the rest of your life. But regardless of whether or not you attend this life-simulator, you're going to have to start getting your act together and taking responsibility, which is why the behavior of this 18-year-old, despite her tragic background, needs to desperately be adjusted.

This stepmother has been really struggling to develop a closer relationship with her 18-year-old stepdaughter, who has not adjusted well to her blended family, saying horrible things about her stepmother, who she has known as a parental figure for most of her life. This tragically complex situation is probably a signifier of some underlying trauma that the young woman is dealing with, but it prompted the stepmother to turn to this online community to see whether or not she was in the wrong for telling her stepdaughter to leave their home, to which the young woman complied.