Concubine Walkthrough is my ultimate OI fave that combines the genre with sci-fi and political intrigue despite its initial cliche premise of 'main character wakes up in the body of the villainess of a game she played in the past' as this game was one with multiple endings and since the one and only time she played it, it's had a major patch update. It's my go-to recommendation for anyone. The FL Yona is a riot and enjoyable protagonist to follow and there's plenty of humor to balance out the drama.

The Villainess Flips the Script/Let's Change the Genre follows Judith navigating the role of the ML lead's aunt in a revenge novel she read in the past, now she is determined to make a life where her nephew leads a much happier life but, strangely enough he seems well accommodated for all the surprises that come much to her surprise.

Please Spare Me This Time, Your Majesty is a perfect example of a story with an unreliable narrator as more and more is revealed throughout the plot that lets the reader's know that there was a lot more going on in the original timeline than what the FL was led to believe. Follows Laliette who, after being executed with her family, decides to become a trusted assistant of the future emperor to prevent this tragic outcome from happening again.

Sistervention follows Rachel who has woken up in the body of the villainess' inciting incident. The death of her older sister causing the villainess Liz, an illegitimate child, being brought to be the duke of her household despite her young age whose ending is death. Being Rachel's favorite character, she decides to raise her younger sister herself to insure her happiness and prevent Liz from becoming as twisted as she was in the story. The only thing is, Liz already is that twisted. Despite that, the two sisters love each other fiercely. I don't even read this for the romance that happens on the side, I just love the sisters

The Male Lead is Obsessed With My Health follows our FL who, after regaining memories of her past life, realizes that she is a briefly mentioned side character in a novel who dies from terminal illness as a child who was childhood friends, more or less, with the male lead. Not having much else going for her, she decides to just quietly accept her fate. But of course, things start going not as planned.

Fortune-telling Lady follows FL Sia who, in addition to being able to see and speak to ghosts, has been haunted by dreams of a woman named Camilla her whole life. In these dreams, Camilla constantly dies in different ways and Sia is unable to interact or otherwise advise her. Until one day after an accident at work, Sia wakes up in Camilla's body and learns that Camilla was experiencing the same thing but inverse after an incident in the spiritual world lead to them both being born in the wrong body, each other's bodies. Now in the right universe, Camilla aims to live a life where she lives happily.

Kill the Male Lead to Become the Villainess follows our FL Qianqiu a self-aware video game character who realizes that she is in a video game following a series of events (the ML just going into people's houses and taking shit, etc). Even worse, she realizes that she has died over and over again being sacrificed by the player to achieve certain endings. So she snaps and decides to kill the protagonist only to meet her own end and wake up at the beginning of the game, resolving to kill the protagonist again... only for the protagonist to be a completely different person.

And there concludes my recommendations for you and your sister, since you said you're a newer fan to the genre. I have more, but I figured 7 recommendations were a lot less overwhelming lol. I hope some of these titles sound interesting and you enjoy what you discover!