How can I disown my adult daughter?

This would generally be the type of thing that would be done through estate planning documents, such as a will, or in a trust. In Arizona, as in most states, you must specifically identify a child you wish to disinherit, it must be in writing, and signed by you. There is no requirement, again in Arizona, that you state any reason why you are disinheriting the daughter, just the name, (I would include the date of birth) and the fact that you specifically intend to not leave her any property of money when you pass.

Unless someone else does an adult adoption, she remains your daughter. If your relationship is so beyond repair you want nothing to do with her socially, then you can choose to remain out of contact physically, emotionally and financially. You can have your advance medical directives and estate planning devices prepared to exclude her from having any involvement with decisions about you and your effects. You will need to consult an attorney in your area to effect your wishes properly. Simply ignoring your daughter will not have the same legal effect. As I am not your counsel and you are not my client, I will not share my perspective on whether or not your desire is a wise one for a parent to pursue.

Stop talking to her, don't pay for anything of hers and when she comes on your property call the police and have her arrested for trespassing. Also, make it clear in your will that she gets nothing. She is an adult and you have no responsibility for her.

The term "disown" doesn't match with any legal concepts. Since she is 20 years old, she is an adult and you have no obligation to financially support her. You can draft a will that leaves your property to someone else, if that is what you mean by "disown". I suggest you hire a lawyer.