I agree with the person above me. It's probably her nerves, or her body could just be changing/making her period late. She is mostly likely, pretty almost positively not pregnant.
Hun, she's not pregnant...relax. If you were not naked, how do you think she could get pregnant? Sperm needs to meet and egg. You would have had to ejaculate directly onto her vagina (no clothes) to even run a risk of pregnancy, and that's still not the way people do it when they want to get pregnant....if ya know what I mean. Her period is late for another reason. Most likely due to stress if she is worried about being pregnant. Since her period is due though, she could take a test if she feels she needs to. Seeing a negative result might just make her feel better that her period will start soon. Good luck in the future, but don't worry about this time. :)