The only thing I can think of for the RFE is that besides providing statements from you two, is providing a signed statement from the preparer (and possibly on the Travel Agency Letter Head), stating that he erroneously listed you and her as married. May not work because your fiancée had to sign on the B1/B2 DS-160 that she read through the application and everything in there was correct. It doesn't hurt to try and see what happens. If not, it's better to withdraw the K-1 visa and go through the CR-1 route.
I am also an El Pasoan completing the K-1 visa for my Colombian fiancé after he didn't receive a B1/B2 visa. It seems like if you're a young, single individual with no concrete assets (e.g., a house) or a lucrative career in Colombia, you're likely to get the 214b slip. The only two people I know that got the B1/B2 visa was an eye doctor and an English professor at a University who both had assets (i.e., properties, cars, motorcycles, etc.) and stable careers. The other four that didn't get the B1/B2 visa included an engineering student, a photographer/business owner, a graphic designer, and a conservation scientist. Two lived with their family and two rented, none had assets and only 2 of them earned modestly.
