There may be some differences by code, but in USA the effect includes the statement, "If the inference prevents the fielder from catching a routine fly ball, fair or foul, with ordinary effort, the batter is also out" . With the interference, the ball becomes dead which takes away the ability for a catch, so the batter is out and has completed their turn at bat.In the case you pose, B4 is awarded first base by FC per rule and has completed her at-bat. In the OP, the batter hits a foul ball and has not completed her at bat