I will admit that I'm not a scholar on the subject and mostly just speculating from what I have available to me, but maybe my speculation is better than nothing, lacking another answer.
My interpretation is that Inanna has just matured enough to realize her own majesty, as seen not only by her delight at her own beauty but also by her placing the crown upon her head. In realizing her majesty, she also feels that the me belong rightly to herself rather than to Enki, and therefore she goes to retrieve them.
You may also find this text interesting in the context; it appears to be a more "raw" translation of the original tablets. In particular, it includes the following fragments (that Inanna speak) in the beginning which seem to be missing from your version of the text:
When I have gratified the lord ……, when I have made …… brilliant, when I have made …… beautiful, when I have made …… glorious, when I have ……, when I have made …… perfect, when I have made …… luxuriant, when I have made …… exuberant, when I have made …… shining (?), when I have made …… return, when I have made …… brilliant, when I have made …… shimmering
I quote them as they appear to me to support my interpretation that Inanna has grown to realize her own greatness.
But again, I'm really not very well-versed in Sumerian myth. I hope someone might be able to give a more informed answer.