Here are examples of the word/phrase "stoutheartedness" used in a sentence and paraphrased in a sentence...
I was super impressed by the stoutheartedness she showed.
I was super impressed by the bravery she showed.
She would of had to have a great deal of stoutheartedness to challenge the boss.
She would of had to have a great deal of valiantness to challenge the boss.
Other Examples...