。
She caught onto his real intentions, didn't she.
Literal
She [topic-は] his [genitive-の] true [genitive-の] intention [object-を] sniffed-out [right?-ね].
嗅ぎつける ('sniff out, get wind of') is a 複合動詞 from 嗅ぐ ('smell, sniff') + 付ける ('attach') — vivid metaphor of catching a scent. Used figuratively almost always: catching onto plots, secrets, hidden motives, journalistic scoops. The polite ~ました ending plus sentence-final ね ('right?, isn't it?') gives a conversational tone — addressed to a listener who agrees, or asked rhetorically. The double ~の (彼の真の意図) chains modifiers: 'his + true + intention.'