That was a wise decision to take a week off and just work on the ball. Good news, we have some contractors and instructors-in-training who started writing out some directions for you to teach Molly to put the ball in a backpack. This will be a good skill for you to work on (away from truffles) during the break between this class and Level 2 (begins August 9th).
Molly values possession. We can work with that. Dogs who value possession often are much more comfortable being the ones to end the ball game by putting it somewhere. The key is that it needs to be fun and motivating for the dog to do. That is why advise teaching it as a trick.
We would like you to post an experiment (if you are willing) with your next video. Let’s see what happens if you remove the resistance of giving the ball back and ask Molly to begin searching again while she still has possession of the ball. She may or may not go back to work. If not, no big deal. Just end the session and be neutral about it. She isn’t wrong. We just want to observe what she chooses to do if you ask her to work with the ball in her mouth. Carry a second ball with you in case she drops the one she has while searching. That way you can still reward at the source of the second truffle. You will just leave the one she dropped on the ground and collect it after the session. It’s just there…no big deal. This is purely for observation. Let’s see what Molly’s choices are.
To make a habit of staying at source, start picking up the target before you reach for the ball.
Working on a “show me” in a different scenario is a good plan. All of these components can come together later so you are correct to present that training in a different picture for Molly. You might do that training in a low distraction environment with treat so it is a calm behavior that she can learn in a less stimulating environment than a truffle hunt with a ball involved. Be willing to accept just a few repetitions. She may get bored quickly. Quantity isn’t important. The quality of the training experience is. Use very high value rewards. If she loves her dinner, this might be a nice dinner game to play with her. Let us know how it goes.