Where the only thing she could really 【do 】in the end was get in her car, and drive off.
=Where the only thing she could really do in the end was 【to省略】get in her car, and drive off.
当不定式作表语,其前已经有实意动词do的形式时,作表语的不定式符号to经常可以省略,用作动词原形.因此,这句中使用了get,而不是to get.
What she could do then was lie down and weep.
注意：固定句式
sb can【 do nothing】 but 【do】
sb【 have/has no choice】 but 【to do 】sth
祝你开心如意!O(∩_∩)O~~