There was a dog missing in the woods up North in NH last year. She heard from people that they saw a dog fitting her description hanging out near a certain area of the woods. So this woman went there and left some of her dirty clothes (clothes she had worn - not cleaned). Apparently, the dog picked up the scent and stayed where the clothes were. The woman went to see if her dog was there, and sure enough he was.

If you think that was your dog at the park, why don't you try leaving some of your clothes there? She may hang around a familiar scent and when you go back to the park, she may be there.

It's worth a shot. Good luck.