Why release her?
Maybe Federal Protective Services (FPS) thought that US Attorney is very unlikely to file charges against her...So let her go with a warning...If this happens again, FPS will arrest her and ask US Attorney to file charges...Just my theory...
This stupid lady is talking tough now...But, will she try to stop ICE agents again? Who knows? It is possible that, if she does the same thing again, Feds will arrest her...Then she will have to show up in front of a federal judge...
Federal prosecutors like to get their ducks in a row before actually filing charges. Indictment will likely follow especially now that she is squawking to the media.