While it’s impossible to know what her role will be like in Transformers: The Last Knight, she does specifically say in the video that she will acting opposite Optimus Prime and Mark Wahlberg, which puts her in the company of both of the film’s major stars.
First and foremost, you may not recognize Laura Haddock in her Twitter video, as she has all of her hair.
While it’s still possible that she could be limited to one scene, as she was in Guardians, it would likely be a pretty significant scene.
Her biggest film role to date was in the part of Meredith Quill, the mother of Star-Lord Peter Quill, who died of cancer in the opening scene of Guardians of the Galaxy.