There are very small chances that your fiancee will be able to get B1 visa as this visa has the highest denial rate, especially if previously denied for the U.S. visa. Consulate officers will see obvious immigration intent looking your case as previously denied for K1 visa. Also, even if she would get it USCIS do not like adjustments from B1 to family based green card. The best advice is to marry outside of the United States and apply for CR-1 visa. It might take longer but is the most right legal way according to your circumstances as i think.