A native of Yidu, she grew up in northern China during a turbulent, war-wracked time. In 1211, her brother Yang An'er organized a group of roving bandits. Sometime after 1214, he was killed, and the 20-year-old Yang Miaozhen was chosen as his successor as the leader of a 10,000-strong band. She joined forces with and married Li Quan, another bandit chief.

In 1218, Li Quan pledged allegiance to the Southern Song, but he was never fully trusted. While Li Quan went out into the field on military campaigns against the Mongols and the Jurchen, his wife ruled their base city of Huai'an (outmaneuvering the prefects sent by the Song).

In 1226, Li Quan fought the Mongols, but was defeated and besieged in Yidu. He held out for a year, but Yang Miaozhen's attempts to reinforce him failed, and he surrendered to the Mongols in spring 1227 and switched his allegiance to them. They made him governor of Shandong. The Song responded by cutting off food supplies to Yang Miaozhen. Her troops mutinied, but Li Quan marched to her aid and reestablished control. In early 1231, Li Quan was killed attacking Yangzhou by the Song. After some attempts to find a male leader, his forces placed themselves under Yang Miaozhen. However, four months later, the Song attacked Huai'an. With defeat inevitable, Yang Miaozhen led her troops to join the Mongols, who in 1232 appointed her governor of Yidu. She was succeeded by her adopted son Li Tan, either soon after or after her death in 1250.

杨妙真是红袄军首领杨安儿之妹，人称「杨姑姑」，善使梨花枪。南宋宁宗嘉定六年，金兵袭击红袄军，杨安儿落海身亡，部众便归由杨妙真率领。后与以李全为首之义军会合后不久，与李全结为夫妻，转战淮、莒县、潍县、临胸县一带，继续抗金。嘉定十一年（1218年），随李全投降宋朝；届时李全被封为京东路总管，不久又晋为招信军节度使，夫妻雄霸一方。宋理宗绍定四年(西元1230年，一说1231年)，李全因兄长被杀而叛宋，攻打扬州阵亡。李全战死后，馀众仍由杨妙真率领，并退回山东力求自保，降蒙古。居数年后，因病而亡。

《续资治通鉴》卷一百六十录有：「杨安儿妹纱真，号四娘子，勇悍善骑射。」

《宋史·叛臣传下·李全下》：「杨氏谕郑衍德等曰：二十年梨花枪，天下无敌手。今事势已去，撑拄不行。」

戚继光《纪效新书·长枪总说》：「长枪之法，始于杨氏，谓之曰梨花，天下咸尚之。」