She appeared in the end of chapter 256. The only thing Lili and her sisters did was set up the next plot point and mate with the MC across multiple chapters, while most of the other girls in this series were actively dealing with a worldwide Karu invasion.
So yeah, it's easy for people to forget about the sisters because they're not relevant in the story of the MC trying to defeat the empress besides Lili now. Once the MC defeats the empress, the sisters will become more relevant in the next part of the story since they're the only people that knows where their village is located.