I think your sister is old enough to know --- to spend all h

我把这个句子加几个词 也许你就明白了
I think your sister is old enough to know something better than to spend all her money on fancy goods.
我在know的后面加了个something
直译：你妹妹年纪不小了（你妹妹够大了）,应该能知道做一些比把所有的钱花在买奢侈品上更好（更有价值/更有意义）的事了.
或者,更像汉语,更地道的翻成,我认为你的妹妹的年纪应该知道她不应该把所有的钱花在奢侈品上面.
more than:超过；很,非常；不知是；多于 反义词是 less than
rather than:(要）...而不...,与其...倒不如...;宁可,宁愿
other than:除了（相当于except)；绝不是