Origin: Spanish, Hebrew, Slavic, Japanese
Meaning: a diminutive of Jésusa, the Spanish feminine form of Jésus, derived from Jesus which is the Greek form of Aramaic Yeshu'a, a contracted form of Yehoshu'a (or Joshua) meaning "Yahweh is salvation" or "Yahweh has saved".
Susa (also known as Shush or Shushan) is also the name of an ancient city in Iran during Elamite rule, a pre-Iranian civilization that ruled across much of what is present day Iran, deriving its name from its protector deity Inshushinak, a Sumerian god.
Susa (or Shush/Shushan) is also related to Hebrew shushan meaning "lily".
It could also be a short form of Susanna, as well as a Slavic surname derived from Susanna as well as from Slovenian surname suša meaning "scraggy, scrawny fellow".
Susa could also be short for Susanoo, the name of the Japanese god of the seas and storm, though I couldn't find much information behind the name's meaning.