why are they attacking her

i have 2 pekin females one 9+ and one about a year, 2 african geese males, and a mallard female also about a year..they have all lived together sharing yards food and 2 ponds...for the last week my mallard has been unfindable most of the day only appearing early am and just before dark..i assume she is nesting fertile eggs although we have never seen any drakes visit our ponds...we have seen the geese trying to mate the mallard and younger pekin...but since the mallard has become docile and detached from the mixed flock when she does come to be in their company the 4 of them attack her and wont let her eat or swim with them...why after nearly a year of close companionship between the 5 of them are they now beating up on her...is this a sign of her possibly being fertile?

Waterfowl behavior can be incomprehensible. Welcome to BYC Duck Forum, glad you are sharing this.

I would be most concerned making sure she is safe - is she hiding in a secure area?

Ducks can get nasty with each other if one of the flock has been gone for a while. They need to be reintroduced, as if they were a new member of the flock. You may want her to have her own area - in sight of the others - for a while so that she is safe, has enough food and water.

Is it spring or autumn where you are?

Also, my ducks will sit on infertile eggs, too.

we figured out where shes going shes not really 10 ft from the pond , nearly between the 2 ponds tucked in a little high grass , ironically in a place where my cat climbs above to sunbathe it would seem she has a few eggs, and is a little louder than normal and oddly did a "goose attack" on me when i left her and my mother earlier today which for her is very unusual..i deal with a goose attack every time i walk through the yards, which is only me , dad and cars, always geese tho...if the eggs are fertile would the rest of the flock know do females get jelious if a member can and they cant..the geese have tried all summer to mount both the young girls is it possible if a mallard drake didnt do the deed that one of my geese has..it is early fall here and our first odd behavior with them.shes only been laying (carelessly)for a few weeks and that isnt daily never same place...none seem to like the house my dad built them it is not close to the our houses tho ,they seem to like sleeping at my back door or bteween our trailers