Teen prefers being alone

DEAR HARRIETTE: My 16-year-old daughter is determined to completely isolate herself. She says she doesn’t want any friends, so she acts very mean and disinterested in other kids at school and extracurricular activities. At home, she likes to stay in her room and read so she can avoid spending time with the family. It makes me so sad, because I’m not sure why she is acting like this. When she was in middle school, she had lots of friends and enjoyed spending time with them. I have tried asking her if something happened at school or if someone hurt her feelings, but she insists that everything is fine.