She is good at making up interesting stories.

Literal

She [topic-は], interesting stories [object-を] make [subject-が] skilled is.

面白い話を作るのが得意 — 得意 (とくい, 'strong at') takes が for the skill. The nominalized clause 話を作るの is what she's good at. 面白い (おもしろい, 'interesting') modifies 話.