What Happened?

:confused: I am so confused as to what to do. My daughter who recently turned 19, she was placed in our care through Foster Care at age 6. We adopted her when she was 12. She experienced a wonderful childhood, all the good stuff,family, love, understanding, parties, friends, great schools. She started a job last summer after graduation while thinking about entering college. Close Mother daughter relationship that friends only wished they had with their daughters. Well about a month ago my daughter left for work in the morning and never returned. I found out through a co worker of her, with whom she had known for only a few months that my daughter returned back to her bio family. She never said anything to me. We talked always, about everything.. She never got in trouble, no problems, I am so proud of her, the young lady she grew up to be. So what went wrong?! She refuses to talk to me and will only communicate through texting. My neice and my daughter practically grew up together. My neice tried reaching out to he only for my daughter to say, through texting, never try to contact her again and she never wants to talk to her. I am not sure what to do. While she is an adult, this is such strange behavior for her. I am so worried yet angry and hurt. Any advice... :confused: