Have someone close to you talk with her about puberty issues, if it is uncomfortable to you. She needs information to help her during this time. Also a book can be purchased and is not uncomfortable for her.
Single parent or not teenagers are difficult. Spend lots of time with her and let her know the changes she will experience. Let her know you are there for her and she can talk to you anytime even if she breaks a house rule. Definately address drugs and sex.
