。
She turned down my offer curtly.
Literal
She [topic-は] my offer [object-を] curtly refused.
素っ気ない ('curt, blunt, cold, short') is an i-adjective for an interaction lacking in warmth. The adverbial form 素っ気なく captures how the refusal was delivered — perfunctory, without softening or apology. Often written in hiragana as そっけない when the kanji feels too heavy. The whole sentence captures the kind of dismissive refusal that lands harder than the refusal itself — a stylistic point worth noticing about Japanese politeness norms.