To be honest with you, this girl sounds a little bit fishy to me. Why would she want to to go out with her then tell her about sex? I don't get it. If she really like you, she will not do that at all to you. In my very own opinion, she's trying to use you for her own game by having sex. So personally I will be extremally careful and put a "red flag" on her. Cause my advice is to walk away from her. Other wise, you will regret something for the rest of your life!