This is where the problem can surface. The consular officer can see her previous DS-160 tourist visa application and notes from her past interview. If they notice that she said you didn’t know anyone in the U.S., but now she has a fiancé, they may question when the relationship actually started, whether she was truthful before. If the officer believes she intentionally lied about something important, they can find misrepresentation, which can lead to K-1 visa denial, a possible permanent bar (unless you later qualify for a waiver).
About 13 years ago, my client’s parents applied for a tourist visa and lied, saying their son did not live in the United States. When they arrived in the U.S., they also told officers they would stay in a hotel and that they didn’t know anyone there. Thirteen years later, their son sponsored them for an immigrant visa. During the interview, something surprising happened, the consulate showed them a video from their entry into the U.S. 13 years earlier, where they made those statements. Because of those inconsistencies, the visa was denied, and the officers determined that they had misrepresented the facts. The ban is generally a lifetime ban, they had to submit a waiver in order to overcome the visa denial.