Just read about your Lacey and I can only repeat how very sorry I am that you're going through this . At least you have such wonderful memories of her last day with you-- sounds like she couldn't have been any happier than when you took her to the farm, I'm sure she fell asleep dreaming of all the things she saw and got to sniff on that walk.
I know how hard the next days will be but try to remember all the good times you shared. Her last memories were of that wonderful day and she will be with you again.