请用英语简单叙述一下木兰从军的故事

Hua Mulan is a heroine who joined an all-male army, described in a famous Chinese poem known as the Ballad of Mulan. The poem was first written in the Musical Records of Old and New from the 6th century, the century before the founding of the Tang Dynasty; the original work no longer exists, and the original text of this poem comes from another work known as the Music Bureau Collection, an anthology of lyrics, songs, and poems, compiled by Guo Maoqian during the 12th century. The author explicitly mentions the Musical Records of Old and New as his source for the poem_ Whether she was a historical person or whether the poem was an allegory has been debated for centuries—it is unknown whether the story has any factual basis.