I'm no eggspert--- and my Golden Comet ---- who is a scrawney thing -- you can see her on my page....also lays Jumbo eggs. In the Storey's Guide to Raising Chickens it identifies Jumbo eggs as 2.5 ounces (and up).
Golden Comets are bred to lay large eggs, frequently. Your comet is just doing what she was bred for.
I did worry -- "she is such a little thing--how does she lay such a large egg?" -- but I don't now.
Age, breed, nutrition and living conditions all have an effect. Your hen is at the age where she is laying her largest.
There was a place where I heard that the amount of protein in the diet also has some effect on egg size. I think partly the heavier the hen, the larger the egg to expect.
I should also say that it is one sign that she is in good living conditions.