、。
She wore a green coat with a matching miniskirt.
Literal
She [topic-は] green [of-の] coat [object-を] put-on, it [against-に] matched miniskirt [object-を] was-wearing.
Two pieces of structure here. 着、 uses the bare verb stem 着 ('wear,' from 着る) as a clause-linker — a written-leaning equivalent to the te-form 着て. The masu-stem can stand in for the te-form to chain clauses, especially in narration and formal writing; it sounds tighter and more literary. それに合った is a relative clause: 合う ('match, suit') in past form 合った modifies ミニスカート — 'a miniskirt that matched it [the coat].' The verb 合う takes に for the thing being matched against: 服に合う靴 ('shoes that match the clothes'). はく is the wearing verb specifically for items worn from the waist down — pants, skirts, shoes, socks.