。
She was waiting anxiously for her son.
Literal
She [topic-は] terribly worry-doing-and son [object-を] was-waiting.
The te-form 心配して here links manner to action: she was waiting, and the manner of her waiting was anxious. This 'manner-of-doing' use of the te-form is common in Japanese, complementing its more obvious roles as 'and then' (sequencing) and 'because' (causal). 心配する combines 心 ('heart, mind') with 配 ('distribute, arrange') — the literal sense is 'arrange one's heart,' a Sino-Japanese metaphor for letting one's mind be taken up by concern. 待っていた ('was waiting') uses the standard past progressive.