The kids were playing a game of Catch Phrase awhile ago with Grammie and Grandpa. Staley was trying to get Adelie to guess the word "garbage truck." Adelie knew what Staley was trying to get her to say, but she couldn't come up with the word so eventually she yelled out "trashwagon."
So now it's an inside joke with Grandpa, and he calls her Trashwagon.
My goofy Trashwagon