What is the ruling on my relative's statement "O disbelievers" on Facebook, as she was joking about the conflict between exam time and Friday prayer, and is my saying to her that I fear her words might fall under the Hadith "O disbeliever" considered a fatwa without knowledge?

"The authorities overseeing the organization of exams should not schedule them at the time of Friday prayer. However, whoever does this does not become an infidel by their action. What your colleague did by accusing people of disbelief is impermissible. What you did by advising her is correct, and you bear no sin or responsibility for issuing a fatwa (definition) without knowledge. She must repent from her statement."