。
She was in a position to decide where to go.
Literal
She [topic-は] destination [object-を] can-decide position [at-に] was.
立場 ('position, stance, standing') is a multi-purpose noun for one's social, professional, or argumentative position. The frame ~立場にある ('to be in a position to/of') is a stock phrase, often used in formal or argumentative contexts. 決定できる ('can decide') is the potential form of 決定する ('to decide'); the entire potential clause modifies 立場 as a noun-modifier. 行き先 ('destination, where one is going') compounds 行く ('go') + 先 ('end, ahead').