To solve this problem, we need to visualize Sudha's movements and then calculate her distance from the starting point.

1. Sudha travels 8 km to the South:
- This means Sudha moves downwards on a map or grid by 8 km.

2. Sudha turns to the right and walks 4 km:
- After moving downwards, Sudha turns right and walks horizontally (towards the East) by 4 km.

3. Sudha turns right again and moves 8 km forward:
- Sudha turns right once more and moves upwards (towards the North) by 8 km.

Now, let's calculate Sudha's distance from the starting point.

- Sudha initially moved 8 km downwards, so her position is now 8 km South.
- Then, Sudha moved 4 km towards the East, so her position is now 4 km East and 8 km South.
- Finally, Sudha moved 8 km upwards, so her position is now 8 km North, 4 km East, and 8 km South.

To find the total distance from the starting point, we can calculate the horizontal and vertical distances separately and then use the Pythagorean theorem.

Horizontal distance:
- Sudha moved 4 km towards the East.
- Sudha did not move towards the West.
- Therefore, the horizontal distance from the starting point is 4 km.

Vertical distance:
- Sudha moved 8 km upwards.
- Sudha moved 8 km downwards.
- Therefore, the vertical distance from the starting point is 8 km - 8 km = 0 km.

Using the Pythagorean theorem:
- The total distance from the starting point = √(horizontal distance^2 + vertical distance^2)
- The total distance from the starting point = √(4^2 + 0^2)
- The total distance from the starting point = √(16 + 0)
- The total distance from the starting point = √16
- The total distance from the starting point = 4 km

So, Sudha is 4 km away from the starting point. Therefore, the correct answer is option 'C'.