Attached below, is the image of Melissa's graph.
The reason why the graph is incorrect is that while the domain of the function is all whole numbers, the domain for the graph is all positive integers. Given that the domain of the function is all whole numbers (which includes both positive and negative integers), the proper way for Melissa to have drawn the graph would be to have continue the line all the way from negative infinity to positive infinity. This means, the line should have spanned both quadrant I (+, +) and quadrant III (-, -) and the arrow should have been drawn on the negative side as well.