。
She spent a huge amount of money on her vacation.
Literal
She [topic-は] vacation [on-に] large-quantity [attributive-の] sum [attributive-の] money [object-を] expended.
費やす is a more dramatic verb than 使う ('use'): it implies pouring resources — money, time, effort — into something, often more than expected. 多量の額のお金 stacks two attributive-の phrases: '[a large quantity] of [a sum] of money,' a slightly wordy but valid construction that emphasizes the size of the outlay. In current Japanese it might more typically be 多額のお金 ('a large sum of money') without the extra 多量, but the layered phrasing here lays the emphasis on thick. The に on 休暇 marks the purpose or target of the spending — 'spent on the vacation.'