Mercedes loves to fetch weather in the water or on land, but before she gives me the ball, or what ever she is fetching she chomps really hard on it. If she ever retrieved a duck like this she would destroy it. Tennis balls only last a few sessions, any tips She's 18 months
Are you planing to do field work with her?
I would find some word to use to teach her what you want -- something like SOFT or GENTLE, to let her know you don't want her to cream whatever it is she's bringing to you. Then using correction and praise, it should take root.
You might want to pose this question in the hunting section, they deal with chewing questions on a regular basis.