。
She's on a trip around the world.
Literal
She [topic-は] world-circumnavigation trip [object-を] is-doing.
世界一周旅行 (せかいいっしゅうりょこう) means 'a trip around the world' — 世界 (world) + 一周 (one circuit) + 旅行 (trip). The ~している form marks an action currently in progress: she's currently on this journey.