Answer:
zerriss
Step-by-step explanation:
Since the first verb (streifte) is in the Präteritum, the second verb should be used in the Präteritum, too, because the sentence shows a series of completed actions. Zerreißen is a strong, or irregular, verb, and its Präteritum form is also irregular: zerriss.
"Sie streifte einen Nagel und zerriss sich das Kleid."