hello question about my ducks

Hi everyone I know this is a chicken forum but I found lots of questions about ducks while searching Google for an answer about mine, so am hoping there is someone who can help me with my dilemma? I have kept ducks for 5years now and thought I knew everything about them. But I am a little stumped and can't seem to find an answer anywhere to my problem. Right here's a very quick history. I had in total 13 ducks at the most we had 5 babies which had 3 males which over ran our amount of females so rehomed 2 of the baby males and had only 3 males left to the rest female as times gone by we've lost females and now have only 3 females left and 3 males, we don't want anymore we decided just to allow them to live their Lives out now but the attacks on our females from the males got so bad we have had to separate them, they've been separated for almost 8months and all the males get along fine had bit of a peckin. Order at first but all settled after few weeks. The females seemed fine too but recently one of the other females has been what looks like raping another female. I know she is definitely a female as she lays eggs we always have 3 a day and she quacks. I wouldn't be so concerned but it's my little khaki Campbell who I've had 5yrs and is her mother that she is doing it too and she has really ragged her she has no feathers left on the back of her head and is obviously looking very unhappy. I'm scared she will end up killing her. Which was the whole point of why we'd separated them in the first place as the males had gang raped one of our white Campbells and killed her which is exactly what we want to avoid. I really really would love some help on this matter and any advice on what I can do. I'm very attached to her she is such a character usually.