Have fun! I agree with no weight in her backpack, but you should take a small backpack with water, treats, and her favorite squeeky toy. Will she be off leash? I started my pup at 4 months old at our off-leash area with flat "hikes" of about a mile. He, however, went about 3 miles with running around and sniffing.
He didn't show he was tired, but fell asleep immediately when we got in the car.
He is 10 months old now and we're up to 6 mile hikes with steep hills and snow. Hiking is great fun!