My dog is a thief....

I took Daisy out for a jog tonight. As part of my course we usually take a lap through the park, where I'll let her off the leash to romp around. In the middle of park we saw Tommy and Jetta. We first met them a few weeks ago. Tommy is the owner (or is it really the other way around LOL)Jetta is a sweet, year old black lab, who is very friendly, and, oddly enough, is happy to let Daisy be the the alpha dog. I find that amusing because Daisy is not an alpha dog by any stretch of the imagination. Tommy brings a ball to the park for Jetta; a "squeaky" tennis ball, that my dog Daisy just loves. So tonight Daisy ran over to play with Jetta, then Maggie, a 5 month old labradoodle (who had her own tennis ball) came to join them. While we let the dogs play and chatted Maggie's "dad" and Tommy kept tossing the balls to all three of the dogs. It was starting to get dark, so I told Daisy it was time to leave and started jogging out of the park. Before we got to the road I stopped and put her leash back on her, then we headed out the drive and through the neighborhood. We were a few houses down the street when I noticed Daisy had something in her mouth - a ball, Jetta's squeaky tennis ball that Daisy likes so well. So I guess my dog is a thief!!! I turned around and headed back through the park, and managed to make it the other end just before Jetta and Tommy pulled out of the parking lot. So how do you make your dog apologize for being a thief?? I'm not sure she felt the remorse when I returned the ball... I think she really wanted to keep it!