Next step is to move this fun game into your yard work, using a bumper for carrying, then doing the give and the fetch. I do this with all my puppies, starting at 8-10 weeks on their short walks. Also, if the dog insists on dropping the bumper all the time, try sitting on the ground, teasing and playing with her. With bumper in hand, scurry it around on the ground, getting her to jump at it, grab it and hold it. Send the dog to retrieve on her name.
Fetch means to take the bumper.
Too many people force the dog to learn the commands with the ear pinch instead of reinforcing what the dog already knows. Do the obedience at a different time or with a lot of time in between so she is fresh and up for it again. Force to Sit - use a long leash and choke chain. Just keep saying sit, cuff with hand up under the chin if she goes to come toward you and pull the leash up, holding it tight above her head till she sits. Always the command NO, then the command for what you want.