Our expert says:
If you are on your own, its your place, and you are entitled to refuse to allow your selfish, greedy and dishonest sister to visit at all, and to explain to her that her stealing is totally unacceptable.
If your father covers up for her stealing, then he is foolish and encouraging her to continue to steal what doesn't belong to her. Tell him that the next time she steals from you, and/or you find something of yours in her possession, you will call the police and lay criminal charges against her. Tell him its about time he starts to behave like a man and a parent, rather than encouraging her to be a thief.
And tell him that he will never be welcome as a guest in your home IF he brings her, because you know she will only use it as an opportunity to steal again, with his assistance. If he arrives with her, send him away to take her back home, reminding him that he is only welcome if he doesn't bring his pet thief with him.
APparently she limits her stealing to members of her own family, but your foolish parents will not avoid trouble as they expect, because with their consistent encouragement, she will also steal from others, who will not choose to protect her.
If your elder sister chooses to put up with this theft, that's her decision, though a bad one.
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