。
She'll probably take the dog down to the river.
Literal
She [topic-は] dog [object-を] river [toward-へ] take-along [probably-でしょう].
連れていく fuses 連れる ('take along') with the directional auxiliary ~ていく ('go away from speaker doing X'), giving a clean 'take and go off with' reading. The へ on 川 emphasizes direction toward the river — interchangeable with に in this slot, but with a slightly more vector-y feel. でしょう is the polite hedge, marking the whole prediction as the speaker's guess rather than asserted fact. The casual contraction 連れてく would also be heard in speech.