。
She likes rich, heavy food.
Literal
She [topic-は] rich-and-heavy food [subject-が] like.
こってり is a 擬態語 (state mimetic) describing food that is rich, oily, and full-flavored — the opposite is あっさり, light and clean-tasting. Both words anchor an entire axis of how Japanese eaters talk about food: a bowl of tonkotsu ramen swimming in pork fat is こってり, while a clear sea-bream broth is あっさり. The verb-style ~した turns the mimetic into a noun-modifier — こってりした食べ物 means 'food that is rich.' Like other stative predicates of internal disposition (好き, 嫌い, 上手), 好き takes が rather than を for the thing liked.