Legal Question in Immigration Law in Florida

The short answer is she can be a thorn in your side but ultimately only an immigration judge can order deportation. By thorn in your side is she could call ICE and report your fiance as being undocumented. That said and unless your fiance is an enforcement priority, ICE likely won't seek to arrest her. You may want to contact counsel and determine how your fiance can obtain lawful status and it is in your best interest to retain counsel for the entire process.

There is nothing she can really "do", however, if he entered illegally, then the process for obtaining U.S. permanent residency is going to be a little more complicated, and thus, I highly recommend seeking representation by counsel before you file anything with USCIS.