I don't have enough information to say for sure. It could be fiction, or it could have roots in reality that have been adapted or exaggerated for a particular purpose.
There was some controversy about the mystery of the construction of the Hanging Gardens of Babylon. According to the descriptions in documents [1] and [2], it was generally believed that the Hanging Gardens of Babylon was built by Nebuchadnezzar II, the king of New Babylon, for his queen Mitisy. Mitisy came from a place with beautiful mountains and rivers. After arriving in Babylon, he felt homesick because of the lack of mountains and rivers. Therefore, Nebuchadnezzar II ordered the craftsmen to build this garden according to the appearance of the Medes Mountains. The document [3] also mentioned that the construction of the Gardens of Babylon required huge technical and engineering capabilities, as well as a large amount of manpower, material resources, and financial resources. However, documents [4] and [9] mention a different point of view, which is that the Hanging Gardens of Babylon was actually located in Ninawa, not Babylon, and was built by Sennacherith, the king of Assyria. In addition, the document [6] also mentions that the Hanging Gardens of Babylon may have been a garden built by the Assyrian king Sennacharib for his Ninawa Palace. Therefore, there was no conclusive answer to the mystery of the construction of the Hanging Gardens of Babylon.
Gardens of the Night is not based on real events. It's a work of imagination crafted by the author to tell a compelling tale. The plot and characters are made up to evoke various emotions and thoughts.
The story of Anger Sierra might focus on Sierra's battles with her own anger, how it shapes her personality and the challenges she faces because of it. It could also involve her growth and transformation in dealing with this emotion.