My new pup Djenga is about 12 weeks old now. I am really happy with her. She is turning out to be a very hard pup, seems like she is also going to be very dominant, but that's not a surpise, her mother and all the females before her are as well. She is very confident and has great prey drive, and I take her out a few times a day, for a few minutes each time, to play with the ball on a string (I hook it on the end of a leash since I don't have an agitation whip). She caught onto this really well and loves it. But sometimes (maybe 1/3 of the time?) when she catches the ball, instead of playing tug she'll get the ball, hold on to it, and then roll over. It reminds me of a "death roll" that alligators do, and it was funny the first couple of times, since everyone compares their pup to an alligator and now more gator behavior. But now it's getting old. She might roll 3-4 times at once. I know I shouldn't reinforce her for this and I don't let her win till she stands up and pulls, but usually I have to pull her up to her feet using the ball. Is this something to discourage, and how exactly should I do this? Or should I just ignore it?

She's a puppy.