Geese are very complex creatures and it would not surprise me at all if your "rejected" goose is feeling jealous. The gander has made his choice by the sound of it, but he may also mate with the second goose, especially after the first one goes broody.

I've never seen a goose attack another goose, but last year our very mild-mannered Pilgrim gander tried to drive off one of the geese. We had to pen her separately when they were confined at night in case he hurt her. In the daytime she just avoided him, but she was very unhappy. My problem was that I had only one gander to three geese. He was crazy about my Buff goose, tolerated the younger goose but totally rejected the third female. We found a new home for the Buff goose where she is now "queen of the barnyard" and much loved and our gander soon accepted both the remaining Pilgim geese. The three are very happy together and I anticipate no problems when mating season begins.

Keep an eye on your geese to make sure no one is getting hurt - especially at night if they are closed in for safety from predators. A low partition with separate food and water for the outcast will keep her safe until all the foolishness of breeding season is over.