She was in the courtyard when Dumbledore's body fell.
She immediiately tried to rationalize the image away. She knew it was coming, he knew it was coming. Ratonally, she knew Draco would be dead otherwise, and with him, Snape.
She tried to rationalize.
It didn't work.
It took Theo tackling her out of a curses' path and the terrifying words-
"Is that the Seer? Let's nab her?"-
- to snap her out of her shock.
It would take several more months for her to work through the image of her Headmaster falling from the sky. But she would.