I would get her on a clicker if she is not already www.clickertraining.com
When she picks up a toy, get up and go toward the toy box (she will likely follow you). When she is near the toy box click and offer a bit of food. She will drop the toy and take the food. Build on this.. the point is the dog already naturally picks things up and sets them down on other things (in this case the couch). Now you want her to pick them up and put them somewhere specific.
Next you use the clicker for teaching the dog different itiems. Start with what she knows (toys) and when she picks up her toy say the word. Repeat it and pretty soon she will know what toy is. Next use a different item she wants to pick up (like a ball.. of course the other toy she is picking up can't be a ball) and when she picks it up say Ball and she will learn what ball is.
Once you figure out how to break the behavior into a little steps leading to the over all thing you want, you can train this dog to do anything.
BTW your guests should be HONORED that your dog thinks enough of them to bring them her toys, dog slobber and all!