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She's worried because she hasn't heard from her son for months.
Literal
She [topic-は] son [from-から] how-many-months [also-も] news [subject-が] does-not-exist [because-ので] is-worrying.
何ヶ月も is the 'many months' construction — 何 ('how many') + counter + も ('also, even') gives 'many X / quite a few X.' Same pattern: 何時間も ('many hours'), 何度も ('many times'), 何回も ('many times'). 便り ('letter, news, word') is the noun for 'news from someone' — common in collocations like 便りがない ('no word [from someone]'), 便りを出す ('send word'). The frame ~から便りがない ('no word from X') captures the worry of an extended silence.