Katabati al-marʾatu still has the noun al-marʾatu as its subject. Katabti has a subject-pronoun tāʾ and is a different form altogether.
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A Kasra Does Not Change the Subject
Feminine Tāʾ in the Past Tense: Form and Agreement
Katabati al-marʾatu still has the noun al-marʾatu as its subject. Katabti has a subject-pronoun tāʾ and is a different form altogether.