According to some sites Zaniah is a Christian/Hebrew name that means "God hears" and it is a short version of Azanaya. It is not an Islamic name. The closest Arabic word Zaaniyah, which means "woman who has unlawful relations with a man", and since this word has a very negative meaning, it is not used as a name.
As for using Zaniah with the Christian/Hebrew meaning, many scholars do not like using names from other religions (since Muslims have enough good names already), and since it is close to a very bad word (Zaaniyah mentioned above), it is better not to use this name.
Zaniah could also be a misspelling of Zaina (also spelled Zainah), which is a good name whose details you can see here: Zaina