Nether Portal Creation/Enter Nether/Creates Another Portal

While on my realm and away from anyone else on the realm, my friend and I built a nether portal to head into the Nether. She went through it, entered the Nether and then proceeded to come back to enter the Overworld and another portal was created in the Overworld about a couple hundred blocks away. This hasn't happened before as we would make a portal, enter the nether then go back through the same portal and end up at the same place in the Overworld.