I feel obligated to suspect that Simmons realized she made herself forget a secret daughter that she left behind with Fitz since I’ve been running with that theory for most of Season 7, but I also find myself suspecting that she remembered something awful that happened to Fitz.
Although Simmons was sad that her fix for the Zephyr came at Enoch’s expense, her breakdown was clearly connected to something else she was remembering, and she was panicking to the point that she couldn’t answer any of Daisy and Coulson’s questions.