。
She probably went to Kyoto.
Literal
She [topic-は] Kyoto [to-へ] went [explanatory-でしょう].
のでしょう combines the explanatory のだ ('it's the case that...') with the polite conjectural でしょう ('probably'), producing a hedged, reflective probability — 'I imagine the situation is that she went to Kyoto.' Without the の, 行ったでしょう would still mean 'probably went,' but it would feel more like a flat guess; のでしょう invites the listener to consider the inference along with the speaker. The directional particle へ on 京都 emphasizes movement *toward* the destination; に would also work and would lean slightly more toward arrival, but the contrast between the two is subtle and often interchangeable in modern Japanese.