It would probably be best to keep her in an area where she can't use her leg to allow it to heal without straining it too much. 
And 8 week old drake is too young to mate, but it could be the shock of being attacked may have resulted in some kind of diarrhea-ish reaction. I would definitely keep the ducks separated from the chickens for now. What are the genders of the other two ducks? The average male duck needs 2-4 females to be happy, otherwise he will target any other female bird around.
	
		
			
		
		
	
				
			And 8 week old drake is too young to mate, but it could be the shock of being attacked may have resulted in some kind of diarrhea-ish reaction. I would definitely keep the ducks separated from the chickens for now. What are the genders of the other two ducks? The average male duck needs 2-4 females to be happy, otherwise he will target any other female bird around.
 
	 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		