She was cramming the last few books into her already full backpack.

cramming 是动词 cram 的现在分词形式。cram 的意思是"塞满、硬塞"，常用来形容把东西强行塞入一个已经快满的空间里。这个词带有"匆忙、勉强"的意味，暗示动作很急促。