If I wrote the name "Brie Larson" on a piece of wood and casted it into the movie, it would've gave a better performance. Marvel and her tried to go for a "I'm a tough girl so I got to act all serious" and it flopped. It would be the same if the character was male. With this in mind, Brie Larson was basically a robot on camera when it came to emotions.
Besides her lacking performance, the story was very shot too. That's what happens when you retcon and try to shoehorn a new character like this before Endgame. I've heard there are talks of editing her out as much as possible in Endgame because of how poorly this movie is doing with critics and movie goers. I'm not surprised.