The farthest we have taken her is 5 miles at a 12 minute per mile pace.

Are we over doing it with her or is this OK? She always seems to enjoy it and once in a while she will wear her Ruff Wear Approach Pack to carry our water, cell phone, keys, etc. Her pack is never loaded down.
We just don't want to do any damage to her. A friend of ours also told us not to take her on runs that long because it will build up her stamina and she'll never get tired and will use her extra energy as aggression. Is that true?
Thanks!