。
She stocked up on large quantities of flour and oil.
Literal
She [topic-は] flour [and-と] oil [object-を] in-large-quantity bought-and-stocked.
買い込む (かいこむ) is a compound verb: 買う ('buy') + 込む ('to put in deeply, to load up') = 'to buy up, to stock up.' The 込む suffix adds a sense of thoroughness or excess. 大量に (たいりょうに, 'in large quantities') emphasizes the volume. 小麦粉 (こむぎこ, 'wheat flour') breaks down as 小麦 ('wheat') + 粉 ('powder/flour').