Can I marry my fiancée overseas and still bring her on a K1 visa?

No, K1 visas are available only to persons who are planning to be married. If the marriage occurs, you will have to file an I-130 Relative Visa petition for your spouse. The one exception to this rule is that if the marriage was religious or social ceremony only, and the marriage wasn’t registered with the local government, a K1 visa may be issued.