。
In the end, she ended up marrying him.
Literal
She [topic-は] in-the-end him [with-と] marry [it-came-to-ことになった].
A double helping of fate-flavored grammar. 結局 frames the outcome as the closing tally of events; ~ことになった ('it came about / it was decided that') describes the result as something that emerged from circumstances rather than from her own deliberate choice. The contrast with ~ことにした ('decided to') is sharp: ~ことになる removes the agent from the decision, treating the outcome as 'how things shook out.' Together with 結局, the sentence has a quiet 'somehow it all led here' quality, the kind of phrasing that feels destined or, depending on tone, slightly resigned.