Dog question

This is probably a stupid question but I'm not very dog saavy, I love dogs but for one reason or another I've never had one. Some of you who know me might know that we have a cabin in the woods, and the local dogs are free to roam at will. Never a problem with that, it's great actually, we get dog visitors all the time. This time the Blue Healer we call "Digger" picked up a ball that had been sitting around for years and dropped it in front of my wife. So now we cut to the chase, how much is too much? Even though I've never had a dog I do know they can chase a ball all day "in theory", but she's bullet fast and panting like mad after a bit. So, when is enough, enough? Do you throw it for 15 minutes and make sure there's a good recovery time? Also she should be in the Majors, she can one hop a ball better than Jeter on his best day ever :D