The correct answer is D. Urticaria multiforme.
The physical exam and findings suggest urticaria multiforme. The patient expresses pruritus, acral edema, positive dermatographism, and transient lesions and importnatly she is otherwise well.
Serum sickness-like reaction the patient is more ill, and has had recently been exposed to antibiotics. The patient has fever, joint pain, etc.
Erythema multiforme is less pruritis, lesions are not transient, and they are often less edematous than those seen here.
Staphylococcal scalded skin syndrome is an exfoliative infectious disorder in which there is superficial desquamation.
A morbilliform drug eruption will have a medication history and it will lack the annular, edematous plaques seen here.
Shah KN, Honig PJ, Yan AC. Urticaria Multiforme: A Case Series and Review of Acute Annular Urticarial Hypersensitivity Syndromes in Children. Pediatrics. 2007;119:e1177-1183.