My child is now 21 year old young woman, but acts worse than 15 year old teen. Why?

She avoids me, does everything to ignore me, she is reclusive, unreachable by phone, text, email and meanwhile she communicates with her "friends" the ones she meets at dance parties every weekend. I see her talking to 1000 people on fb, yet when I sent her a simple "hi, how are you" message she does not bother to reply as I don't exist. She moved out 7 months ago, and eventually stopped talking to me. I have no clue what she up to , unless spy on her on fb....we never had a falling out or a big fight. We had somewhat normal rel-p. I am single mom and gave her the best I could, all I could. Good school,good home, good food, love, devotion. Why she is so cold towards me?