No it wasn't. For example, why only Rika could see her? Don't tell me "lol it's just the way it is, the plot lol"
And why couldn't she turn human all those years and all of a sudden she turned human? And what does the process of turning in to a human involve? Does she get born out of a tree trunk or a rock? Or does some pregnant woman give birth to her in the hospital like any other human being? Tell me which episode explained that.
But then, I'm expecting you to just go "lol it's all explained in the anime, and those that aren't, it's just the plot, the way things are! lol!"