This can cut the cycling time in half. I've cycled a system this way in 6 days! As long as you're sure the water source is safe, as you could inadvertently import fish/plant diseases form "dirty" water. Your friend's system has "seeded" water with nitrifying bacteria in it already, so adding to water with an ammonia source(your system) the bacteria will have food to continue growing. Nitrifying bacteria can double in size, under the right conditions every 24 hours. Good luck!
yes it is the fastest way to cycle. You can get some aquarium water as well if you do not have access to aquaponic seeded water.
you'd be better off getting some of her media (gravel/hydroton whatever)
just trade some of your unseeded media for her seeded media
Yep, that's a great way to speed up your cycling process!