There seems to be massive confusion on this site and in the general public about what actually constitutes miming and lip synching. Miming is when you are consciously trying to convince an audience that the vocals they hear are coming straight out of your mouth. Nicki does not and never has done this. She sings the singing parts of her songs live, accompanied by the studio version and when shes raping she usually does it without the studio version.
In that sense she has done nothing wrong, however I am disappointed in her for showing up so late without apologizing to her fans.