Do you mean how many eggs will you get or how many batches will the goose lay and incubate herself?
I would expect her to lay every other, or an egg every three days, from late feb, till june (ish). So probably 30-40 eggs a season. If you let her sit than thats the end of her egg laying for the year. I would be inclined to incubate them in an incubator myself, some geese are terrible mothers.
If you introduce a new goose you'll get more eggs but I have had issues with egg pinching when one goose is sitting on eggs and another goose wants to lay an egg. They will literally roll eggs from under the other goose, so you end up with the batch split between 2 nests and with them getting cold and dying.