Why did Heartfulness cause friend's sudden irritability and mood swings?

My friend started the practice to manage stress, but now she is losing her temper easily and is prone to sudden, severe irritability. She was previously very calm. I am worried that the required slowing down of her mind is triggering a psychological resistance, causing intense mood swings and increasing her underlying anxiety. Her name is Rima and her birthday is on July 1st, 1993. Time: 6:15 PM. Location: Chandigarh.