In Mario & Luigi: Bowser's Inside Story, Starlow is sent to Princess Peach's meeting as a representative of the star sprites. Starlow believes that the cause from The Blorbs was from Blorb Mushrooms sold by a man in a gray cloak. Later, she is inhaled into Bowser, along with Mario, Luigi, and other citizens of the Mushroom Kingdom. She can combine her powers with Princess Peach to levitate people, such as Bowser, and also help Mario and Luigi to perform certain action commands. Starlow often talks to Bowser from inside of him to give him information. Starlow uses Chippy as her name for Bowser, not wanting him to know that she is helping the Mario Bros. She also helps Mario and Luigi in their encounter with Bowser. She can also save the player from nearly unavoidable attacks from bosses like Bowser, the Dark Star and the Dark Star Core, by having Mario and Luigi grab her feet so she can fly up to the top screen.
Starlow appears to have negative feelings towards Luigi, and this negativity towards him sometimes generates humorous results, such as when Starlow angrily knocks Luigi into Alpha Kretin after Luigi suggests that Starlow fight it alongside Mario rather than him. The reason Starlow feels this way about Luigi is unclear, but it may have something to do with the boss battle with Scutlet inside Bowser's body, where one of Scutlet's attacks was throwing Starlow at one of the brothers to cause damage, which had to be countered with the brothers' hammers, after which Starlow would jump in anger while facing either the brother that countered the attack, or Scutlet itself if the attack was not countered. Assuming the player made successful counters to this attack with only Luigi, Starlow may resent Luigi for this reason.
At the end of the game, when Bowser hears Starlow's voice, he easily recognizes her as Chippy and gets furious, deciding to pick a fight with the Mario Bros. and her. When Bowser and Peach's Castle were remodelled, Starlow and Birdley deliver a present to Bowser from Peach as a thanks for all he did, and they have a small chat, ending with Starlow teasing him and him yelling at her to leave his castle, which she does.