We have had nothing but trouble since she was very small. We adopted her and her brother she was 4 1/2 her brother 3 1/2. She has attachment disorder (my belief), diagnosed with conduct disorder. She has been arrested for property destruction at one residential facility and assault at another. She was in jail for 2 months for assault.
We thought she had learned her lesson and we picked her up after the lawyer got her off with no bond just probation. She has pending court cases. Now she is up to her old tricks, stayed out all night and we didn't know where she was. She had walked to the mall to meet a boy (10 miles away) who would not come and pick her up and he took her out of town and she did not have a ride back. Her grandmother had just given her $20.00 which I'm sure she bought drugs with. When she finally did call I told her she needed to find some place else to stay because we didn't want her at home anymore. but we are sick of her upsetting our lives. The police then brought her back saying that it's against the law to kick her out. Our son (her brother) who we have also had trouble with was listening. The next thing I knew the police left with her. So I am not sure what's going on. But finally my question is why is it against the law to kick out a child who is 18? Why does the law enable these people to be freeloaders?

Since you adopted her your state may require you to care for her until 21
Otherwise you have to do an eviction according to your state laws.

When did the police bring her back and what happened that she left with them?
Is she still gone since then and how long?

Oh and what state/country are you in?

Missouri / Cole. I don't think so because the adoption subsidy and medicaid stop at age 18. The officer didn't even ask if they were adopted he just said you can't just kick them out at any age.

You can't just kick out someone legally living on the premises. You would have to go through a formal eviction process.