The condom advice is gold but something I tell kids who are sexually active is that all forms of birth control have a failure rate. If you'd rather not get pregnant than use some form of birth control. If you really don't want to get pregnant use more than one.
Make sure you wear a condom and make sure you know how to PROPERLY put one on. I'm sure you don't want to be a father just yet. Maybe she should get on some form of birth control too.
By offering to wear a condom