Paderborn is generally very safe for solo female travelers. It's a small, university town with a low crime rate. It's generally safe to walk around even at night. The locals are friendly and helpful, and there is a fair amount of English spoken due to the university and a British military base nearby. While normal precautions like not leaving your belongings unattended and avoiding dark and secluded areas at night should still be exercised, Paderborn is considered safe.