Her book admits that it was a two-level lie from the beginning (emphasis mine here and throughout). 

We had to make these palatable to the administration by avoiding the obvious appearance of a full Italian lockdown. At the same time, we needed the measures to be effective at slowing the spread, which meant matching as closely as possible what Italy had done – a tall order. We were playing a game of chess in which the success of each move was predicated on the one before it.

Further: 

At this point, I wasn’t about to use the words lockdown or shutdown. If I had uttered either of those in early March, after being at the White House only one week, the political, non-medical members of the task force would have dismissed me as too alarmist, too doom-and-gloom, too reliant on feelings and not facts. They would have campaigned to lock me down and shut me up.

In other words, she wanted to go full CCP just like Italy but didn’t want to say that. Crucially, she knew for sure that two weeks was not the real plan. “I left the rest unstated: that this was just a starting point.”

Fifteen Days to Slow the Spread was a start, but I knew it would be just that. I didn’t have the numbers in front of me yet to make the case for extending it longer, but I had two weeks to get them. However hard it had been to get the 15-day shutdown approved, getting another one would be more difficult by many orders of magnitude. In the meantime, I waited for the blowback, for someone from the economic team to call me to the principal’s office or confront me at a task force meeting. None of this happened.

“No sooner had we convinced the Trump administration to implement our version of a two-week shutdown than I was trying to figure out how to extend it,” she admits. 

White House Covid Coordinator Deborah Birx Describes How She Tricked Trump and Brought Lockdowns to America