。
For me, she's the most important person.
Literal
I [for-にとって] she [topic-は] most important person is.
にとって is the compound particle for 'for [someone], from [someone's] perspective, to [someone].' Marks the perceiver or judger of a subjective statement. 最も ('most') is the formal/literary superlative marker — a written-register alternative to 一番. The whole sentence has a slightly elevated, considered tone.