。
She loves her son deeply.
Literal
She [topic-は] son [object-を] deeply is-loving.
愛する ('to love') is a strong verb for romantic, familial, or principled love — stronger than 好き. Often used in its ~ている form for ongoing love. 深く is the adverbial of 深い ('deep'), used metaphorically here for 'deeply.' 息子 ('son') is the standard term; for one's own son one might also use うちの息子, while addressing him directly often uses 息子 + name or simply name + くん.