Relax - she's a puppy. Puppies do all sorts of goofy things - that doesn't immediately equate to a poor sport prospect. My sport dogs roll over for belly rubs, drop their ears when they get hugs, give kisses, sleep on my bed, and let puppies chase them around. That doesn't speak to a lack of ability on the field.
As long as the pup is not showing overt signs of submission - such as urination, ears back constantly, tail between legs, pitiful whining, eyes out of focus, etc - the pup is likely just playing