“It’s your choice.” She shrugged. “You can continue with your worthless life, or you can become someone who matters.”
Do not capitalize the second half of a compound sentence. Just because you could break it into two sentences if you deleted the comma and the conjunction doesn’t mean it is two sentences. (Maybe that’s not why some writers do that, but I can’t think of any other reason right now, and I would like to think there’s a reason for it, even if it’s wrong.)
The first sentence could also be written this way: “It’s your choice,” she said with a shrug.
(“It’s your choice,” Mercenary Proofreader said with a shrug. “You can stop using impossible verbs when describing how dialogue is spoken, or you can continue looking like a fool.”)