。
She put fresh soil in the flower pot.
Literal
She [topic-は] flower-pot [into-に] new soil [object-を] put-in.
植木鉢 (うえきばち) combines 植木 ('potted plant') with 鉢 ('pot, bowl'). 土 (つち, 'soil, earth') and 入れる ('to put in') form a straightforward action. The に marks the destination — the pot is where the soil goes.