Keira used to weigh 23kg before she was neutered, her record was 7 hours of running next to me as i cycled, and we only went home because i felt like i was going to pass out haha. She was super fit.
Now she is 4.5 years old (neutered at just over a year) she is 36kg... (she is a chunk of muscle, pic below) and she slows right down after the first half hour.
I would not worry over nothing, as long as she is in good health (cant feel spine/hip bones), her weight doesn't matter. There are small huskys as well as the odd chunky ones.