Method 1:
After turning 90°, She is looking in the East direction, then after turning 135° in the same direction, she would be facing the southwest direction. At last, after turning 270° she would be facing the northwest direction.
Method 2:
Taking clockwise direction as positive and anti-clockwise direction as negative,
90° + 135° - 270° = -45° => 45° anticlockwise which is Northwest.