。
She's been traveling abroad.
Literal
She [topic-は] outside-country [path-を] travel-and-came.
国外 ('outside the country, abroad') is a formal, slightly written-leaning word that pairs naturally with its mirror 国内 ('within the country'). 旅行してくる combines する-verb 旅行する with the directional auxiliary くる ('come'); together they mark 'traveled and came back to the speaker.' を on 国外 marks the path or area traversed, not an object — same pattern as 道を歩く ('walk along the road'). The te-form ~てくる indicates motion toward the present location, framing the trip as something completed and returned from.