I don't believe that you can fail to portray a character, because on my experience, I have met people in reality very much like Ran. She is just portrayed as your ordinary girl, crybaby XD. Besides, she kinda has a right to be that way since the guy she likes has been missing for months. I don't really read too much into character development in general because if the author wanted them to be any other way, then they would of just made them that way to begin with. Sometimes her personality actually influences cases as well, so there could be a deeper meaning into her being the way she is. All together I find it impossible to think of a char as annoying so long as they don't have an irritating voice or insanely ugly. Without having false facts, it is impossible to write a story incorrectly. Just go with the flow XD.