A few short walks are better than long ones until she is at least 8 or 9 months old, or even a year. If you have a garden, let her play and free run as much as she likes although if she is getting tired out, say by playing with another dog or kids then you should intervene.
Walking on a lead takes far more out of them than free running.
Certainly no more than about 15 minutes at a time for at least the next couple of months, or else you will end up with a weak, scrawny, leggy, Bambi type setter, with no bone or substance. Good food and gentle exercise will allow her to grow to her potential.
If in doubt, check with the breeder who should be willing to give advice on things like this.