Two points.
First, as I suspected, in checking both Pipes and Figes source notes, neither read , or at least acknowledged, Ambassador Francis's book. It is pretty rare and took us a decade to find. So they may account for their not knowing about his report. I can't lay my hands on our copy of Meredith just now, so I can't check his source notes.
Second, Kerensky did write such a book. "Russia and History's Turning Point", 1965, Meredith Press. It is fairly self serving in nature and should be read with a skeptical eye and cross referenced with more "un-biased" accounts. His account of the incident:
"I decided to take a big risk and drive all the way across the city. This was part of my normal routine, to which everyone was accustomed. When the fast car I normally used arrived, we explained to the army driver what to do. At the last moment, just before the acting commander of the Petrograd military district, my adjutant, and I left, some officials from the British and US embassies arrived on the scene and offered to drive us out of the city under the American flag. I thanked the Allies for their offer, but said that the head of the government could not drive through the Russian capital under the American flag. As I later learned, however, the car turned out to be useful for one of my officers who could not fit into my own car. It drove a distance behind us."
His footnote to this paragraph: "Lies and slander are often quite indistructible. Even to this day foreigners occassionally ask me, with some embarassment, if it is true that I fled from the Winter Palace dressed as a nurse! That foreigners should believe this utter rubbish is perhaps forgivable. But it is quite extraordinary that this story is still p;u out for popular consumption in the Soviet Union. The more serious historical works published in Moscow give a factually accurate account of my departure from Petrograd to Gatchina, but in a vast number of popular histories the same story is repeated over and over again to fool the people of Russia, and also the people of other countries, that this, that I sneaked away dressed in a woman's skirt."
I think he did commandeer the car, as pointed out, "borrow" implies a return, which was rather unlikely. Second, the Francis's reports were sent back to Washington, and so are extremely accurate in their nature and Francis has no reason not to report what he knew exactly. I do, though, believe that the report of the nurse uniform was a Soviet bit of dis-information to make Kerensky look like a coward when faced with the "courageous" and "victorious" Bolsheviks. Just my 2cents.