I would suggest that you take this very seriously and seek the assistance of a qualified immigration attorney to determine the best course of action for you and your fiancée.
While it's possible, it's not a good idea to enter the US on a different kind of visa while your K1 application is still pending because this puts your K1 visa application process at risk.
Now that your fiancé's situation has come to light, her K1 visa application will be closely examined. Take this extremely seriously because it may also make it more difficult for her to obtain a future visa to the US.
