Final answer:
The original sentence lacked punctuation and has been corrected by adding a semicolon to separate two closely related independent clauses.
Step-by-step explanation:
The sentence provided needs punctuation to separate the clauses. The corrected version of the sentence should be: "I've never seen Brooke Osmond fly or walk through walls; she keeps her powers a secret." A semicolon is used because it connects two independent clauses that are closely related in thought, and no coordinating conjunction is used.