She caught a cold and is losing her voice, so she can't give the talk.

losing 是动词 lose 的现在分词形式，lose 的意思是"失去、丧失"。 her 是代词 she 的所有格形式，表示"她的"。 voice 是名词，意思是"声音、嗓音"。 losing her voice 是一个固定表达，字面意思是"正在失去她的声音"，实际指"嗓子哑了/失声"的状态。