For leave it there is actually an easier way then the way that you are trying. You start with holding a treat in your hand, show your hand with the treat to your dog but don't let her have it (closed fist best to start with), when she's sniffing it you tell her to leave it and the minute she looks away from the treat she can have it. I always say take it when I'm giving the dog a treat just so they know that they can have it.

Evntually you can work up to having an open hand with the treat on it, the treat on the floor, dropping the treat on the floor and walking Gigi past it. Leave it is also good with other dogs and stuff. Also remember at first that as soon as she takes her attention away from the treat she gets it, it can be just a glance or even if she stops sniffing the hand she can have it.