。
She is worried about her son's health.
Literal
She [topic-は] son [genitive-の] health [object-を] is-worrying.
More direct than the のこと-padded version of the same theme — here 健康 itself is the direct object of 心配する. Both ~を心配する and ~のことを心配する are correct; the latter feels slightly softer/less direct, while the former is more compact. The choice can be a stylistic call. ~ている marks the ongoing worry.