legally adopted?

Is there a legal term of 干女儿 in English? How does he introduce her to his friends? Did he adopt her legally? Does he claim her as a dependent in tax returns? Was he part of the hosting arrangement for exchange students? By any defination, she is an adult, an adult blessed with family wealth.Most college kids have to worry about summer jobs and summer interns. Unless she jntents to abuse the opportunity, or she is clueless.