From what I have seen with my ducks ( I have had a lot) the big one should get use to them over time. It might take some time. I only have one that had to be kept separated for good. That one was eventually gotten rid off.
I had always wondered. I know this is not a goose but I have a khaki duck that is 7 and still lays in the summer. Her production has gone down due to age.
I have read best production is up to 6 years. I have a 3 year old buff and she is still laying well. I would have to flip though my goose book again to be sure though.
You can try putting up a fence or something to stop the others from pushing her out. Just make it big enough that you can put water and feed in for her.
A lot of roosters are like that but not all. In my experience with the roosters that start being that way they don't stop. For me they go away for good. We had one rooster that would always attack my dog (us too) and my dog would grab him by the neck hold him down until the rooster stopped...
I currently have an American buff hen and a super African hen. Mine are housed at night by themselves but free range with my ducks and chickens during the day. Mine have never wondered away. The only time I have had problems were with the ganders during breeding season when the ganders have...