
Firstly, I'm so glad your girl has been given the all clear re her bladder infection, that's great news.
Regarding excercise, I have a GR pup here, almost 14 months old now, who would have been having 2 to 3 walks a day of about 15 - 20 mins each at around 5 months. I spent a long time taking her on her own sometimes, and at other times with my other two, but didn't let her off lead with my big male (who is very rough when playing!) until she was at least 10 months.
I would let your pup have some off lead time as long as she doesn't get knocked or encouraged to race around by other dogs. I always found a gentle older dog always promotes calmer behaviour, I would walk my pup with a neighbour's two elderly Irish setter bitches and it worked a treat! She learned good doggie manners which has served her very well.
At the end of the day, they have to have an element of fitness and build up of muscle to protect their frames. Without the "core" fitness, they are much more likely to hurt themselves if they take a tumble or twist. It's a delicate balance, as little or no real exercise could leave them vulnerable to injury. Try to avoid your pup becoming too overweight, and give her several short walks a day rather than one long one.
My pup now, at just over a year, is extremely athletic! I often think she gallops just because she loves it so much, loves jumping on/off things (not something I encourage, but logs etc in the woods are just about ok), she could keep up a pace for an hour at least, although more likely 45 min walks, and is still normally bouncing at the end...
Good luck, I'm sure she's absolutley fine, and she'll tighten up as she matures.