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She is extremely worried about her son's exams.
Literal
She [topic-は] son [genitive-の] exams [genitive-の] thing [object-を] extremely is-worrying.
心配する ('worry, be concerned') takes its target with を when expressed as a clause-noun via こと: ~のことを心配する ('worry about X'). The のこと is doing important work — it nominalizes the topic, making 'the matter of son's exams' a discrete object of worry. Without のこと, you'd need a more direct phrasing. ~ている marks the ongoing state of worry. 非常に is the formal/written intensifier ('extremely'), stiffer than とても.