(Spoiler Alert) I feel that Kagari is the by-product of a timeline where Okabe and Kurisu have a baby now I say this for one of 2 reasons. First, in Steins;Gate for characters with discernable faces and important roles, they have a reason for being part of the story and usually either connect to Okabe or Kurisu. Second, There is no way that Kagari is going to purposely look like Kurisu just for plot convenience, plus even if true there seems to be a usual resemblance to Mothers and daughters in this anime. The examples would be Yuki and Suzuha and I'm talking about the first appearance of Yuki in Steins;Gate Episode 24 which is an Ova and also a continuation of episode 23. This is only a theory one that runs off how the flow and feeling of the anime and Game. If you don't understand what I mean watch the Anime or a walkthrough of the games and you will see why I say what I say.