This is a rather unusual and uncomfortable situation. It's important to remember that hentai manga often present fictional and exaggerated scenarios that aren't based on real health advice. You should encourage your sister to seek professional medical help instead of relying on fictional depictions.
I'd say this is not something to rely on hentai manga for. The real solution is to take your sister to a doctor. A medical professional has the knowledge and expertise to handle this properly and offer the right advice and treatment.
Chapter 606, "Are There Crocodiles?!", is the clearest early answer because it turns Ji Yanbai's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Hearing Ji Yanbai volunteer to stay behind, everyone ceased to have...
Chapter 586, "She Just Likes Men Who Show Weakness Initiative", is the clearest early answer because it turns Yu Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Yan quickly swam over to the person.
Chapter 328, "Persuading the Old Master", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Jiang Li's authoritative words stunned the old man.
Chapter 409, "I'm Feeling Lucky!", is the clearest early answer because it turns Nina's situation into a concrete plot event. It opens with Jiang Yan was still arguing with Yu Li with his hands on his hips,... and closes on She has been staring at you since just now." Jiang Li took a look at....
Chapter 291, "To Hell with Sister Complex!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 387, "Hello everyone, this is my disciple", is the clearest early answer because a shaky connection becomes usable in the plot. A useful checkpoint is the way the scene starts with Liu Suqing V: "Even if we meet, I wouldn't recognize, faces covered...
Chapter 288, "The Old Master Already Knows", is the clearest early answer because it turns Senior Su's situation into a concrete plot event. The chapter gives readers a real answer by opening on Jiang Li and Zhao Lang were lifted onto stretchers and taken to...
Chapter 438, "The Upper Stream is Mine, The Lower Stream is Yours", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with I'm sorry," Shang Shuyue squeezed out three words through clenched...
Chapter 390, "Is Jiang Li Commended by the Police Again?!", is the clearest early answer because it turns Sister Li's situation into a concrete plot event. Early on, The bell rang for school to let out, and Tao Ying hurriedly grabbed....
Chapter 291, "To Hell with Sister Complex!", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event. The chapter turns that into something concrete by moving from Early in the morning, Jiang Li's hospital room door was knocked.