In reply to Flinticus:
Hi there,
Kelp is probably able to do much more than 3h of hill walking in a day, however I doubt it will be safe for her to do so.
Too much exercice on growing dog can alter they development, especially bone growth and joints. Walking itself isn't so bad but pups are pups and it's all the running and jumping that is especially strenuous on the joints.
As mentioned earlier, she'll be fully grown at 18 month old, before that I would advise to walk her a little and often : something like 30min walk 3-4 times a day should be OK, and still avoid making her jump over fences or wall.
A good way to use her energy is by doing some training, and teaching her tricks. Collies are really good at that and you should have good fun teaching her.
Take it from the vet