。
She prayed for her son's safe return.
Literal
She [topic-は] son [genitive-の] return [object-を] prayed.
祈る ('to pray, wish, hope') takes the prayed-for outcome with を. 帰還 ('return') is a Sino-Japanese compound — 帰 ('return') + 還 ('also return'), giving an emphatic 'safe return.' Common in wartime contexts (兵士の帰還 'soldier's return') or for return from long, dangerous trips. The pairing of 祈る with 帰還 carries a sense of anxious waiting — a parent praying for a child away at war or in distant peril.