What can I do if someone hacked my social networking account?

What you should do immediately is change your password so she no longer has access on her phone. If your personal items have been posted anywhere online, file reports with those services to have the items removed. What the girl did may be a federal crime of intercepting electronic messages and making those public. You may want to have a lawyer explain this to her and have her destroy all copies off everything she intercepted. She needs to learn and grow up and this sounds like the perfect time for her to learn that lesson. You also need to learn to be much more careful with security over your accounts. It is usually a mistake to lend or borrow a personal phone or computer to access emails or social media. Get online and read about that and develop habits that you will use for the rest of your life. If you are being bullied by this girl and her friends, talk to a teacher or counselor today.