Explanation:

- Original Sentence: She is more witty than her sister.

- Option 1: "wittiest than" - Incorrect. "Wittiest" is a superlative form, used for comparing three or more items, and does not pair with "than."

- Option 2: "more witty then" - Incorrect. "Then" is used to refer to time or sequence, instead of "than" for comparisons.

- Option 3: "most witty than" - Incorrect. "Most witty" is a superlative, which is inappropriate with "than."

- Option 4: "wittier than" - Correct. "Wittier" is the comparative form of "witty," correctly used with "than" for comparing two people.

- Option 5: "No correction required" - Incorrect. The original phrase "more witty than" is improperly structured for comparative use.