Not only did she introduce me to her friends but she also introduced me to her brother.

not 是否定词，表示"不"或"非"的意思。 only 是副词，表示"仅仅"或"只"的意思。 not only...but also... 是一个固定搭配的关联词组，表示"不仅...而且..."，用于强调两个并列的事实或情况。