My gf is here on a K1 visa..Can we take a short trip to mexico and come back?

The K-1 entry is only for one entry and for 90 days. You would not be allowed to take a short trip to Mexico and come back. The proper way would be for you to be married, have her apply for her adjustment of status to permanent residence, and at the same time apply for advance parole to travel outside the US during the time that the adjustment of status application is pending. It usually takes 90 days from the date of submission for an advance parole application to be approved.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.