two cents from a father of a nice Kid. a 20 yr old son.
Communication is key. Never dismiss their thoughts or ideas no matter how different from yours. Validate them before presenting what you feel is a better alternative.
Rules of the house HAVE to come with communication of what the consequences are BEFORE the rulles are enforced. i.e. curfew is 10 pm. if you are not home by then consequence is one week of no computer. Then, most importantly, you must administer the punishment as promised. Do that a couple of times and she wont cross the line again.
What is not fair is if you make up the punishment AFTER the crime is committed. Shows no consistancy and her thoughts are ,"well, its not fair and he is out to punish me".
always view EVERY event as a teaching moment. How you act, speak, punish. She is watching you and watching you closely.
Also talk about how good decisions lead to more opportunities in the future. More options. A better life is one full of options. i.e, make the decision to get better grades leads to more options for college and lifestyle.
Poor decisions on the other hand, lead to less options. Decide to have sex can lead to getting disease and/or pregnancy. results in less options for freedom, school, guys (most guys wont date a 16 yr old mom).
finally the "wanting to feel better about herself" as the reason for having a boyfriend is very dangerous. indicates possible lack of self esteem. Is she getting encouragement from you? mom? Do you make her feel good about who she is?
Generally, girls who are easy are ones who feel who they are is not enough for a boyfriend therefore they must "put out" in order to have one. If she wants a boyfriend (a good one!) have her state before the relationship that under no circumstance is anything sexual going to happen. this will immediately seperate the good guys from those who want in her pants. And yes, at 13, sex is VERY prevalent. (just look at her pictures)
Ask her how she wants all of her friends to view her.... as a nice friend or a skank. Her actions will decide that.
Sorry about the frankness, but being frank, open, and honest will reward in the long run.
Good luck
oh, forgot, there is a book called "the strong willed child" by Dr. James Dobson. Best book I ever read about raising children. (or managing people too for that matter).