Repeated failures never weakened her resolve; in fact, they made her stronger.

weakened 是动词 weaken 的过去式，weaken 由形容词 weak（虚弱的）加上动词后缀 -en 构成，表示"使变弱"或"削弱"。 resolve 在这里是名词，意思是"决心、坚定的意志"，指一个人做出决定并坚持到底的心理状态。