Here are the recommendations from the Hovan Slow Growth Plan, which is generally very concerned about good joint development. From looking at this, it sounds like walking 2-3 miles on a leash is no problem for a pup her age, especially if you work her up to it gradually. Happy walking!
Taken from
http://www.jrsgoldenangels.com/slowgrow.html
Exercise Recommendations
Exercise is a vital component of the Slow Grow Plan. An active puppy can eat more food, and thus will be more
assured of getting enough nutrients. Furthermore, his muscle-to-fat ratio will be more favorable, reinforcing the
desired goal of a slowed rate of growth. And the stronger muscles will properly support the skeletal system, which
combined with greater coordination, will help protect him from injury.
Free-walking is a suitable exercise for dogs of any age, because it permits them to choose their own pace and level of
exertion. Of course, this must be done in a safe environment. While this may not possible on a regular basis for most
people, perhaps it can be a special weekend treat. And walking on leash is certainly an acceptable alternative.
Begin with approximately 1/2 mile walks with the 8 week old pup, 4-5 days per week. Add about 1/2 mile every other
week. If you fall behind schedule, do not jump ahead to make up for lost weeks. Instead, resume where you left off.
If there has been an extended layoff, begin back several weeks and build up again, as below. An exercise level of 3
miles per day, 4-5 times per week, will result in a fit, healthy puppy. Of course, as with any exercise, be very cautious
in hot weather; cold is rarely a problem.
8 wks. old = 1/2 mile, 4-5 times weekly 14 wks. = 2 miles, 4-5 times weekly
10 wks. = 1 mile, 4-5 times weekly 16 wks. = 2-1/2 miles, 4-5 times weekly
12 wks. = 1-1/2 miles, 4-5 times weekly 18 wks. = 3 miles, 4-5 times weekly
Do not jog, bike, or otherwise roadwork a young Golden under 4 months of age. Prior to beginning these types of
more stressful exercises, it is advisable obtain a preliminary OFA hip evaluation. Only puppies with a preliminary
rating of “Good” or above should be considered candidates for this more serious athletic training. Always build speed
and distance very gradually.