My normally calm cockatiel suddenly screams whenever I leave the room

I've had my cockatiel, Kiwi, for about three years, and she's always been pretty chill - chirping softly and enjoying her toys while I work from home. But over the last week, every time I leave the room for even a minute, she lets out these loud, piercing screams that startle me and the neighbors. I’ve tried leaving the radio on softly and placing a mirror in her cage to keep her company, but nothing seems to help. I’m worried she’s feeling really lonely or anxious, but I’m not sure if it’s something else like a health issue or a sudden change in her environment. Has anyone else experienced this sudden shift in their bird’s behavior? What helped calm your cockatiel down when they started screaming after being left alone? Should I be looking into any specific health check-ups or environmental tweaks?