My motivation behind this question is that I want to translate the Chinese word "学妹" into Japanese. 学妹, as you probably have guessed already, refers to a female 後輩. A male 先輩 is 学长，female 先輩 is 学姐，male 後輩 is 学弟. However, it seems impossible to be gender specific when using 先輩 or 後輩, since these word encompass both genders. So what is the appropriate, natural word for a female 後輩?
Edit: Sometimes, 学妹 can be used flirtatiously. That is, sometimes, you can be more flirtatious by calling the girl 学妹 instead of using her name or something. I cannot find the word that has this usage in Japanese, so that's a better explanation of my motivation.