That's a baseball in the picture..Shelby tends to destroy tennis balls rather quickly. One thing I noticed, when the temperatures are 60 degrees or higher (yesterday it was 77 here), Shelby is only good for a few dozens throws before she lays down and quits all huffing and puffing. She may not have the ball drive like some GSD. Your suggestion using a racket with a tennis ball is a good one and I may consider that in the future.
There are also other tools for getting distance on a tennis ball. There is a toy called a Chuck It that you swing and there are sling shots and there's even a special golf club called a Doggie Driver ()