Plus, she could still call in sick, no? What job fires you for taking one sick day? Admittedly it’s quite a coincidence she gets sick on the day for which she asked for and was refused an absence. Too bad she had to miss a day of work and her graduation day.
And in the meantime, she should be looking for a job with better work conditions, which she can now get, due to her graduating college.
That being said, it’s pretty assured that this letter is fake.