I belive Amy was in a trance, and could only imagine people who died recently. Mclntyre died a while ago, Erasmus was a sad loss, but Amy might've forgotten about him. Then there is Grace and Hope; they were real flesh and blood! I think this is the reason, but I'm not honestly sure.
I think Amy just simply cared about Grace, her mom, and Evan more than the others. You also have to reneged that this isn't real and authors are doing their job quick and sloppy because they have the pressure of a million fans. Not that I would do a better job than them without God's help because that is a lot of pressure