。
She whispered softly in my ear.
Literal
She [topic-は] softly my ear-side [at-で] said.
耳元 (literally 'ear-base / ear-vicinity') is a compact noun for the area right next to someone's ear — the spot where you'd lean in to whisper. The 元 suffix on body parts is productive: 口元 ('around the mouth'), 足元 ('around the feet, where one steps'), 胸元 ('around the chest'). The で here marks where the action of saying happened, the location-of-action particle. そっと is a 擬態語 (state mimetic) for hushed, careful, inconspicuous action — covering the manner of the speaking without specifying its volume. Japanese rarely uses a dedicated verb for 'whisper' (though ささやく exists); 言う + そっと does the work just as effectively.