The only way to know if she's pregnant is to take a test. And as far as not getting her pregnant I agree with everything @Bree61714 said. Get her on birth control and use protection.
Don'r exactly understand what you just said in the beginning. But safe ways to avoid pregnancy, would to stay protected! You kinda answered your own question. Wear condoms, get her on Birth Control, use spermicides, and if you had unprotected sex with her less then.3 days ago, get the plan B pill. It is roughly around 50$ and they have it at your local drug stores. Must be 18+ to purchase it. She has to take it before 72 hours of you all having unprotected sex.