The correct option is B, SENTENCE 4.
In English language, a parenthetical element refers to a word or group of words that add non-essential information to a sentence or a clause. A non-essential information, is an information that a sentence can do without, that is, without that information what the sentence is saying will still make sense.
Looking at sentence 4, the parenthetical element there is 'her old friend'. If this phrase is removed from the sentence, the sentence will still make sense.
The sentence ought to be written this way: 'She hoped Darlene, her old friend would be there.
If the parenthetical element is removed, then the sentence become: 'She hoped Darlene would be there.