Was Naori Uchiha the creator of Izanami?
Although never explicitly mentioned here's a possible explanation. Before that however, there are a couple things to consider.

Firstly, the cost/consequence of using either technique leads the caster's sharingan to loose its light immidiately
Secondly, Both techniques enable users to change reality. In the case of Izanagi, the illusion is applied onto reality itself. While in the case of Izanami, the caster is able to put an individual in an almost sentient never ending illusion which becomes the reality of the opponent, continiously, until some trigger is met. (i.e the opponent either changes their ways or is trapped in an eternal loop)

Now the point I'm trying to make here is that I believe that the Izanami is a variation of the Izanagi which attempts to save a person by creating a repeating loop of specific events until some criteria is met. Thinking about it in the broad sense it still classifies as changing reality but only for the opponent because it will always work regardless of the opponents 5 senses, even if they know its an illusion.
So yea I believe she is the creator of Izanami, nevertheless, considering the similarities both have. It seems to me that she creatively used the Izanagi to such a degree that was completely unthought of (using it to help an individual change and thus creating a variation of the izanagi to stop the izanagi hence the izanami).