If she is wild for the food, use that now. You know she loves the ball so using food will allow you to work on the ball rewarding away from truffles.
You have a couple of options for working on the ball game.
1- You can play a two toy game where she gets the one you have when she OFFERS to release the one she has. You will still need to have treats for the final time you take both balls away (unless you teach her to “put it away”. My dogs put their own toys away for a treat.
2- You can teach her to put the ball in your backpack for a treat. I highly recommend you do this. Not only does it give Molly and “end of reward” and “start hunting again” cue, it gives her the power to release the ball herself instead of you taking it away from her. I can’t take a ball away from Callie but she is not actually resource guarding it. She simply doesn’t want the fun to end. By adding a fun trick of putting the ball away, she happily drops it in my pack for some treats and then goes off to hunt again. There is no pressure involved in the entire sequence. Every part is rewarding.
It will be valuable later for you to be able to work with toys and treats so this is a great time to work with treats while she wants them and sort out the best toy reward option for you and Molly away from truffles.
You may even consider working with treats and ending with the ball, making it very clear that you are done hunting. Then she can keep the ball.