Qing princess, a daughter of 皇太极, married to 吴应熊, son of the general 吴三桂. 金庸's novel 鹿鼎记 makes her Kangxi's wild younger sister and a wife of 韦小宝, which is how most Chinese know her.
Lìshǐ shàng de Jiànníng gōngzhǔ qíshí shì Huáng Tàijí de nǚ'ér, búshì Kāngxī de mèimei.
The historical Princess Jianning was actually Huangtaiji's daughter, not Kangxi's sister.
Tips
history
The real princess was Kangxi's aunt: his father, the Shunzhi Emperor, was her younger brother. During the Revolt of the Three Feudatories led by 吴三桂, her husband and their son 吴世霖 were executed, in 1674.
history
建宁 was a title, not her name: in 1659 she became 和硕建宁长公主, and the title was later changed to 恪纯. Literally, 建宁 is 'establish peace' and 恪纯 'reverent and pure'.