Attempt 1 · one-liner

> write a thank-you email to a donor

Attempt 2 · four-part brief

> [role]      You are my development assistant.
[context]   Donor gave $15k to our youth literacy program,
            their second gift. Warm but not gushing.
[example]   Match the tone of the attached past email.
[constraint] Under 120 words. No dashes. No superlatives.