。
She picked an apple for me.
Literal
She [topic-は] me [to-に] apple [object-を] plucked [for me-てくれた].
もぐ is the lovely, slightly old-fashioned native verb for 'to pluck' (fruit, flowers) — the action of grabbing something off a stem with a quick twist. Less common in modern urban speech; 取る ('take') and 摘む ('pick') are more general everyday substitutes. The image is bucolic: someone in an orchard reaching up and twisting an apple free. リンゴ is conventionally written in katakana even though the kanji 林檎 exists, following the modern convention of writing many fruit and vegetable names in katakana.