First of all, don't trust snakes around Missy. She may or may not defend her nest. But the snake may also not seem BIG enough, or move fast enough, to really make her worried. So I'd play it safe, and assume that she WON'T defend the nest against them.
Second, buy moth balls. More than one box. Sprinkle them all around Missy's enclosure. Snakes do not like the smell of moth balls, and will avoid getting near her because of the moth balls. Try not to put it where the goslings can get to them once they hatch. I doubt Missy will touch them, but the goslings might. So if Missy is in a pen, put the moth balls around the ENTIRE outside of her whole pen. They don't need to be piled up on each other, but a few inches apart or so will make the smell strong enough to deter snakes. And the scent alone, in an open area like that, won't become concentrated enough to actually cause any of your geese or goslings any harm. As long as they can't eat it.
Although one suggestion I once read was to get a bunch of 2-liter bottles, and poke holes all in them. Then put some moth balls in each one, and place them on the ground or hang them all around the enclosure. The snake still smells it and avoids it, but the geese and goslings can't get to it to eat it.