。
She finds fault with anything and anyone.
Literal
She [topic-は] anything [at all-にでも] anyone [at all-にでも] complaint [object-を] attaches.
文句をつける is the active 'pin a complaint on,' a touch sharper than 文句を言う ('to complain') — it suggests deliberately seeking faults to register. 何にでも・誰にでも doubles the universal quantifier with にでも attached to interrogatives, conveying 'absolutely anything, absolutely anyone.' The repetition does pragmatic work: it paints the pattern as exhaustive and habitual, the kind of person whose nitpicking has no limits.