If she spends her entire allowance in the first week, she'll have nothing left for the rest of the month.

allowance 是名词，由动词 allow（允许）加上名词后缀 -ance 构成，本义是"允许给予的东西"。在这里特指父母定期给孩子的"零花钱"，通常指固定金额的零用钱。