Grayson was only in one scene in this episode. It falls about 20 minutes into the show, if I recall aright.
My theory is that the episode was filmed in Fla. (the company apparently toured the US and different episodes were filmed on location, or so I have read) and GH did it there on her way home from Mexico. Of course she could just have easily done it in LA which is actually closer to Puerto Vallarta as the crow flies.
G.