All you can do is to tell her to really think about what she's about to do because once she crosses that bridge, she cannot go back! Tell her that sex is something special and she needs to think about the consequences. Ask her if she's ready to be a mother, be pregnant, or be faced with the decision of having an abortion or putting a baby up for adoption and tell her that by having sex, she's putting herself at risk for that. Condoms are not 100% effective!! Not even the pill is 100% effective, but saying "no" is!!