You might be looking at the wrong set of trees. As silly as it sounds, I made the same mistake. Here's what do. When you exit the park to go to town, look to your right and at the very end of the sidewalk is trees and a cardboard box. Check in there like if you looking for any other unplugged friend. You'll find her(?) eventually.
Pokemon Pearl Name and Friend Code: ButzPuff 3265-1552-2983