I adopted my child when she was 3 months old and she will turn 2 next month. When do you think I should tell my daughter that she is adopted and how should I do it?

The truth has to be spoken someday and there is no perfect time to break the news like this. My aunt and her husband adopted my cousins since she was born. They took care of everything including her legal issue and plan to tell her by the time she was married. So her real father can give her blessing and marry her (we are from moslem family)