They also have a copy of the official letters from BK.
Sometimes an employer can over-react to comments on Facebook, but in this case I don’t think Burger King is over-reacting. She directly slagged her employer off in a public forum.
If she had not named the employer, then that would not be an issue. Likewise if an employee just posts about a bad day at work, then an employer might be over-reacting to take action. But the comments made by Tyler undermine the good faith needed in the employer/employee relationship.
As it happens, she was also on a final warning for swearing and customer relations.