FWIW. God will often choose people powerless and completely unsuited to various tasks. This we can see for example, with the apostles, common fishermen, with David vs. Goliath, with Noah building an Ark, with Abraham in eldest age having children, and so forth. He does this to demonstrates that it was not by the natural power of a person that one thing or another was accomplished -- In St. Joan's case, putting an end to the Hundred Years' war.
They're an example of the work of God.
Are Abraham and Sarah an example that you should wait till you're 90-100 to have children? Is Noah an example that everyone should ordinarily build giant boats in the middle of dry land? Or David an example that featherweights should go fight to the death vs. heavyweights?
No. Therefore the exceptional nature of the matter shows it's the work of God, His direct intervention. What was accomplished was by the power of God, St. Joan was the sign this was the case because she was just a young maiden, for whom leading an army to success in war was not something she could in any way accomplish, or something at all reasonable a circuмstance to place a young maiden in, save by divine fiat or one might suppose the most unusual and hard to imagine absolute necessity.
Whenever she did things that were not normally proper for her state it was with proper extenuating circuмstances, and in a way that still was not intrinsically immoral, but properly exceptional however unusual.
That modern people raised in a degenerate society take her as a role model for various immoral actions and roles for women is their own fault.
Remember that God designed the Church, government, and the family, and everything inbetween all to be patriarchies. Patriarchy is good. You'll find the natural roles more surviving in places where corrupt entertainment has not filtered in as greatly, much criticized for it Middle Eastern countries, etc.