I think your pup understands what you want...but only refuses to do it when you don't have a treat, right? If that's the case you need to slowly wean her off the treats..and I KNOW it's easier said than done I have a Lab/Beagle mix who is ALL about the food!! What I would do (and have done with my own dogs) is to ALWAYS have treats in your pockets, and I mean always. (its useful for teaching a reliable recall too!) However, she doesn't get a treat EVERY SINGLE time she sits, only once in a while so it keeps her on her toes guessing when she'll get a treat. For the times you don't give a treat praise, praise, praise. Also keep the training sessions short and sweet but practice MANY times throughout the day (remembering to only give treats once in a while, the ultimate goal is to eliminate the treats and have a dog that will respond well to praise, again easier said than done!), I'd have her sit before she eats, sit before she goes out or comes in, etc. Good luck