Greta's brain.

But now, if she did know about the surgery...

“Yes, I had a surgery a few years ago. I had almost the same symptoms as this one and Josiah helped me remove the tumour. I was fine, until the tumour started showing its ugly face again.”

Camila closed her eyes for a second, understanding better now. Greta knew she was operated, but she thought it was to take out a tumour and not to put something in her brain

Who was lying to her?