One of the biggest misconception about Joan of Arc is that she was an idiosincratic dreamer who was a loner with the head in the clouds and was different. While it seems more that she was a bubbly and normal girl, a people person with a lot of energy, kinda rebellious but in an outright way, not an imaginative and reclusive way. She did not seem really idealist either, she was very ethical, but she was not big idea oriented, she just wanted to serve France, serve the king, and expulse the english. Actually, she was ESFP.
One other big misconception is that an IFP must wait to be 60 years old to start using Te, and that an EFP must wait until 30 to start using Te. The truth is that we all use the 8 functions to some degree. But IFP are Te inferior, meaning that they need a lot of balance to take control of their environment in a logical and impersonal way, and usually fail to do it. And this is true at every stages oftheir life. While EFP are puerile Te user, meaning that they can quite easily be bossy, assertive and controling, but are unpredictable and don't follow easily through a stable and steady plan. Also, this is true at every stage of their life.
Obviously, Joan of Arc was in the second case. But I think she was ESFP, the voice she heared was her inferior Ni.