。
She has to take care of that elderly man.
Literal
She [topic-は] that elderly-man [genitive-の] care [object-を] do-must.
世話をする ('to take care of, look after') is the standard collocation for caregiving in any sense — children, the elderly, pets, plants, even hosting guests. ~なければならない is the textbook construction for obligation ('must do'), a compound built from the negative conditional ~なければ ('if not') plus ならない ('won't do'). It feels formal in writing; in casual speech, you'd more often hear ~なきゃ or ~ないと. The sentence carries a faint weight of duty — caring for elderly relatives is a burden the language treats as inevitable, often falling on daughters and daughters-in-law in traditional family structures.