It is not normal. Like @aart stated, chickens are not supposed to lay two eggs in one day. That puts a lot of stress on their body and can easily make them have issues if an egg damages the vent, or the pressure having to push out both the eggs makes her prolapse. Definitely not a normal thing that is supposed to happen. A one-off double yolk egg is not harmful because, while it may be larger than normal, it does not have a significant difference and certainly cannot be likened to the pain produced by laying two eggs at once.It is normal that a pullet can lay 2 eggs in a day. They can also lay double yolk.
They sometimes lay 2 eggs in a day, double yolks, and tiny little eggs. Not unusual at all.