。
She poured her heart and soul into it.
Literal
She [topic-は] that [in-に] heart-and-soul [object-を] poured-in.
精魂 (seikon) is a noun for 'energy of spirit, soul, full effort' — 精 ('essence, vigor') + 魂 ('soul') compounded for emphasis. The collocation 精魂を込める ('pour one's soul into') is fixed: 込める ('to load, to pack in, to put into') with abstract nouns of feeling and effort. Productive parallel idioms include 心を込める ('put one's heart into'), 力を込める ('put strength into'), 思いを込める ('put one's feelings into'). The に on それ marks the recipient or container — 'put it into that.' Slightly literary register; the kind of phrasing you'd see in a memorial speech or admiring biography.