。
She successfully crossed the Pacific Ocean by ship.
Literal
She [topic-は] ship [by-で] Pacific-Ocean crossing [in-に] succeeded.
~に成功する means 'to succeed in' — the に marks the accomplished goal. 太平洋横断 packs 'Pacific Ocean crossing' into a single compound noun: 太平洋 (Pacific Ocean) + 横断 (crossing/traversal). This compression of verb phrases into compound nouns is highly productive in Japanese, especially in formal and journalistic contexts. The で marks the ship as the means of transportation.