This is not because the Third Sister knows that Leia is Anakin Skywalker's child; it is because the Third Sister found a link between Obi-Wan and Bail Organa and she believed Obi-Wan would do anything to save Bail's daughter.
Reva knows that Anakin Skywalker is Darth Vader because she was one of his targets—a child—during the Order 66 killings that took place during the events of Star Wars Episode III: Revenge of the Sith.
Reva explained that she discovered a connection between Bail and Obi-Wan in the archives. She doesn't realize that Leia is Vader's daughter. Reva does attempt to use the Force to peer into Leia's mind when she kidnaps her again. However, the little princess was able to defend her thoughts.
Third Sister happened to notice, through her studies of Kenobi, that he was close to the Organas. So she hatched the plan to hire a bounty hunter to kidnap Leia, hoping that would draw out Kenobi.
Sensing Obi-Wan's shock when she mentioned Lord Vader, Reva confirmed Anakin Skywalker was still alive - also showing she knew what had happened on Mustafar. Related: Obi-Wan Kenobi Episode 2 Ending Explained: Where Is Darth Vader?
The Third Sister was at the Jedi Temple during Order 66. She either saw Anakin kill her fellow Jedi or saw the recording of his crimes. That's why she has such hatred for Obi-Wan. She was a Padawan who escaped Order 66.
This is confirmed later in the movie when Obi-Wan informs Padme that Anakin killed them. Both are torn apart with hurt and confusion, trying to make sense of something so terrible.
During the iconic opening moments of Star Wars: A New Hope, Darth Vader has a tense confrontation with Princess Leia, an adversary who, unknown to him, is actually his daughter. Despite participating in Leia's interrogation, the Sith Lord doesn't uncover his familial connection with the rebellious royal.
That's all you get. It's well known that Star Wars lead characters Luke Skywalker and Princess (now General) Leia are brother and sister. The estranged siblings didn't know about their familial relationship until "Return of the Jedi." They even shared a passionate kiss in the previous movie, "The Empire Strikes Back."
The reason Leia likely remembers Padmé is that she could sense her mother's emotions at the time of the senator's passing. Luke didn't possess the same ability as his sister and inherited their father's Force potential. This links with Luke's desire to follow Anakin's Jedi path.
Following the Wampa attack during the movie's opening scenes on Hoth; Leia, Han, and Chewie visit Luke in the infirmary. Leia is annoyed with Han, who insists she has feelings for him, so she kisses Luke to prove she doesn't. Presumably, the scene was simply meant to make Han jealous.
Secret tunnel
Leia is left in the tunnel that leads to the pilot so Tala can help Obi-Wan. Reva also enters the tunnel while Tala is still inside, despite this not only do Reva and Tala never cross each other but Reva gets to the pilot before Leia.
While Leia is denying Han's assertion that she has romantic feelings for Han, Leia kisses Luke passionately to demonstrate that Han "doesn't know everything about women" and to suggest that she has feelings for Luke instead.
Reva Sevander, better known as the Third Sister, is the central antagonist of the 2022 Disney+ Star Wars miniseries Obi-Wan Kenobi. She was a Jedi youngling who survived Order 66 and fell to the dark side of the Force, joining the Galactic Empire by becoming part of the Inquisitorius.
Padmé Amidala (portrayed by Natalie Portman) is the wife of Anakin Skywalker, the mother of Luke Skywalker and Leia Organa, the daughter-in-law of Shmi Skywalker, the mother-in-law of Han Solo, and the maternal grandmother of Ben Solo. She served as Queen of Naboo, and later as a Senator for her planet.
Later, the heroes go to the forest moon of Endor to prepare for a battle with the Empire. There, Luke reveals to Leia that she is his twin sister and that Vader is their father.
While Return of the Jedi would ultimately reveal them to be siblings, A New Hope implied Luke's attraction to Leia throughout, while the two kissed multiple times in The Empire Strikes Back, with further romantic moments ending up on the cutting room floor, as seen in the movie's deleted scenes.
After Leia and Luke's lips lock in Lannister love, our wookie friend vocalizes what seems to be his approval. However in hindsight, Chewie was more than likely saying “Your species' obsession with sibling mating is a curious one, I've seen your browser histories”.
At some point between A New Hope and The Empire Strikes Back, Darth Vader learned that Luke Skywalker is his son, but when did he discover this?
Why didn't Darth Vader recognise Leia as his daughter in Star Wars: Episode IV? He didn't recognize her because he didn't know his daughter was alive, and he couldn't tell it from reading her mind because she wasn't aware of it herself.
While their affection had to remain hidden, the two kept in frequent contact, even throughout the Clone Wars. But despite this, Anakin found out that Padme was pregnant only a couple of weeks before the twins were born. So, why did it take so long for her to tell him?
Star Wars Just Confirmed Darth Vader's Undying Love for Padme Amidala. Star Wars: Darth Vader #23 revealed just how much Anakin Skywalker loved Padme Amidala even after his transformation into the Sith Lord.
In Star Wars canon, there are currently only four younglings that are known to have survived the infamous Order 66 and Darth Vader's slaughter, while in Legends, there are 20 known survivors.
Anakin does not have even the slightest bit of remorse. By the end, he feels nothing but anger. Although he feels regret for killing Padme, he still helps the evil Emperor. The film ends with Anakins standing side by side with the man on whose behalf he has committed all his crimes.
The story is Anakin was manipulated to the dark side by Palpatine based on fears of losing Padme and appeals to his desire power and agency, over his life and the galaxy as a whole.