If i had chlamydia, had sex, and then got treated and had sex with her again after, is it possible for her not to have been infected before treatment?

Tests not perfect: Unclear question. I think you mean you had chlamydia (symptoms and/or positive test) but your partner had a negative test. Chlamydia can clear on its own before treatment, and tests miss some infections. Even with negative test, both partners need treatment at the same time before resuming sex. If this didn't happen, retreatment may be necessary. Discuss with your doctor(s). Best wishes.