The correct option is D everybody is looking at
Option A is incorrect as the restrictive pronoun 'that' has already been used with 'pretty girl' as it refers to the 'pretty girl'. Thus, 'that everybody is looking' is incorrect.
Option B is incorrect as the use of pronoun 'her' at the end of the sentence is not required.
Option C is incorrect as both 'that and which' are not required in the same sentence here, as both are referring to the same clause'.
Option D is correct because when we put an active sentence, where a preposition follows after the verb, into passive – the preposition remains immediately after the verb. Here, "looking at" follows this rule.
Thus, option D is the correct answer.