I think she got that info from Mao's personal physician, Dr. Li Zhi Cui. He wrote a book called The Private Life of Chairman Mao. Here's the Amazon link for his book.

The writer of Mao: the Unknown Story received a lot of flak for that book. A lot of historians say that book has way too many anecdotes that can't be proved... like the story about no showers. There's another story about how he didn't brush his teeth, but just rinsed with green tea. How can you prove that?

Chang and Halliday conducted a lot of original interviews for that book. A number of the outlandish claims in the book stem from these. It's been difficult for other historians to follow-up on them.