Our expert says:
At one level it seems pretty obvious where the problem starts. It IS very early indeed for a bereaved widower to start going out with a new gf only 6 months after his wife's death, and early to start living together only a year later. Whatever his actual feelings, to many people, and apparently very much so to his daughter, this suggests that he hardly loved his wife / her mother, and was keen to move on to someone else.
It sounds as though she strongly resents you and your daughter having as she may see it, taken over her dad, taken over the family home, disrespected her mom, and pushed her to the outskirts.
At 18 she is indeed old enough to refuse treatment she does not want.
And its probably a mistake to see her as the total embodiment of the problem, as someone needing to be fixed. That's not so. The family as it now stands is not well, and dysfunctional, and it is the family and its internal structures, expectations, behaviours, and rules, that need to be fixed. I'd think that trying to force the girl to accept "therapy" as though she has to be the only person in the wrong, and disordered, will be likely to fail. Suggesting that you;re none of you happy as things are and need to negotiate a better way of living together by having shared family therapy from a properly trained psychologist, is much more likely to work.
Like Liza, I'm struck by the invisibility of the father in your story - its his responsibility to play an active and understanding role in trying to sort this out, as it was his choices which started this all off. He can't wash his hands of it.
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