、。
With nothing to do, she couldn't settle down.
Literal
She [topic-は] anything [also-も] thing-to-do [subject-が] not-existing [so-なくて] couldn't-calm-down.
落ち着く is one of those verbs whose negative form does heavy emotional work — 落ち着かない describes the inability to feel grounded, the antsy fidget that boredom and anxiety share. The negative te-form なくて links cause to result here: idleness produces unrest. The construction ~することがない builds the abstract noun 'something to do' from a verb plus こと, the most common nominalizer for actions and abstract events.