This teaches me to post after reading only about ten pages of a book. Let me just straighten this out.
Joan of Arc did NOT keep her voices a secret from all but two people. She told everyone that God had sent her by speaking to her--that's a big part of why they followed her. It's interesting, everyone was skeptical but receptive, the way you would be today if someone showed up in your town sent by the President. It was understood that God COULD send people, but that not everyone who showed up saying God sent them was telling the truth.
What she kept private was the true nature of her visions, voices, and experiences. She didn't explain the bright light she saw, or who was speaking to her (Saints Michael and Catherine, mostly), or how it felt or what was said. Only that God had sent her, and spoke to her.
Still she was practical, and smart. And it's a good book, if you'd like to read it.
I have about 15 library books out now. And it gives me such satisfaction, I can't explain it. It's like having three hundred dollars in your pocket. Maybe even four hundred.