I guess, I'm alone to say that she is the contrast to Haibra; While I adore both characters, Haibara is more of the intellectual genius who lost a family and is regarded as a traitor and is running away from the past. While Ran is the more strong character who is stuck in the past and do not want to escape the past because of emotional attachment. Hence forth, I guess while Haibara wants to stay in a child's form; Ran seems eager to meet Shinichi. In other words Ran is in love with Shinichi the real character, while Haibara is in love with Conan the fake character Shinichi has made up to live. I do not doubt that Ran will end up with Shinichi, while Haibara will end up getting over the matter and find something new. Therefore I guess Ran would be essential for motivating Shinichi to come back at the very end..