“weak sister”别理解成“软弱的姐姐”，真实含义是胆小的、懦弱的、不可靠的人。

【例句】
Don't worry, we reassigned him. The last thing we need right now is some weak sister dragging this case down.
别担心，我们重新分配了他。我们现在最不需要的就是一些不可靠的人拖累这个案子。

I knew everyone on the team thought of me as something of a weak sister, so I spent the whole off-season training and practicing.
我知道队里的每个人都认为我是一个胆怯的人，所以我花了整个休赛期来训练和练习。