The fact that she had underestimated the power of the head of the Makiri family and the insects he commanded might also be to blame.
Her familiars had probably been deliberately overlooked. Numerous insects had been stationed along her route, and Francesca had ultimately been forced to discard her body at the time after being intercepted by a fiend in the form of an old man.
“Illusions don’t work too well on bugs.”
“If only I’d had more time to prepare, I could have fooled the whole region and slipped in that way. . . .”
“Oh, Gilles, Gilles, I hope you managed to enjoy the War.”

Fate/Strange Fake: Volume 6, Chapter 20 ("Dream Becomes Reality")