Oddly, her character is marked as seasonal on the login screen... Could it be because there's another player on the same console (different battle.net account though) that has completed the campaign? Is it possible that allowed her to choose seasonal when she set it up? She can't remember what she chose.
Is it possible that allowed her to choose seasonal when she set it up? She can’t remember what she chose.
Unless the character was created pre-season, there's nothing that would stop her from selecting seasonal realm on character creation. It's also the default for new characters.
The most likely answer is "she created a seasonal character".
No, you can make a seasonal character straight away. The restriction is that you can't access the seasonal content (malignant gems, malignant quest line) until you've finished or skipped the campaign with that character.