we are doing obedience, agilty, flyball, AND dog parks, long walks, etc, and my 5 month old is not slowing down! we can't do too much in a day, because his bones are not fully matured, but lacey does not have this problem. agility is probably the best bet for you, because if you get an instructor that will work with you, you can train in agility to tire her, and at the same time slowly adjust her to stange people. the more she is trained in agility, the more focused on it she will be, therefore, you could have a very odd looking person (judge w/ umbrella, wheelchair confined person, etc) out in the middle and she will not notice (or not care) because she is busy w/ agility.
my other dogs are aslo both very active, and love to run, so they tire him out on their own. you have a newf, so (not to stereotype, but) she isn't gonna want to run run run all the time, like an aussie. sorry....
herding is expensive, but if there is someone with sheep (ducks are not good for dogs w/ preydrive, cattle are scarey for first timers.) that wouldn't mind being harrassed by a wild child, they may not charge you much at all. just ask an instructor for type outs of exactly what to do to train her, or ask them to go w/ you.
hope this helps,
Leah