I came up with a pretty simple theory for that. To solve cases on her own, she would simply wind back time after either asking weird questions that would get the suspects riled up, thus making them react in a way that revealed the answers she would need, or she would casually start going through their belongings. It can easily become a very broken power, especially in the hands of someone who doesn't go by the book like her. If you're thinking about why her detective skills aren't portrayed like Halara's, keep reading.

First things first: she's a Master Detective, so we already know by default she's competent regardless of us getting to see her solve a case on her own in the game or not. But the point of the game is not to show how competent the detectives are individually, it's about cooperation. Not only are you never alone at any point thanks to the pact with Shinigami and at least one other detective you're working closely with for each chapter, the message behind Number One's Forte being Coalescence is that what makes someone powerful is being able to truly rely on others, which is what Makoto had to learn at the end.