>>149813506
Even ignoring how moral support is very important, Jeanne's fellow generals talked extensively about her skill with artillery and siege warfare. She won every single fight where she had access to cannon.
Additionally, she escorted the then Dauphin to Reims so that he could be crowned king, which further weakened the English claim to the throne.
>>149813530
Jeanne is known for all of her prophecies being correct, though she'd attribute this feat to God rather than her acausal nature.