كَتَبْتُ رِسَالَةً.
Meaning: I wrote a letter.
The final -tu itself is an attached subject pronoun.
كَتَبَتْ فَاطِمَةُ رِسَالَةً.
Meaning: Fāṭimah wrote a letter.
The feminine tāʾ (-t) marks gender; it is NOT the subject pronoun. Fāṭimatu is the nominative subject, and risālatan is the accusative object.
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Pronouns: definitions, forms, usage, and parsing
كَتَبْتُ رِسَالَةً.
Meaning: I wrote a letter.
The final -tu itself is an attached subject pronoun.
كَتَبَتْ فَاطِمَةُ رِسَالَةً.
Meaning: Fāṭimah wrote a letter.
The feminine tāʾ (-t) marks gender; it is NOT the subject pronoun. Fāṭimatu is the nominative subject, and risālatan is the accusative object.