。
She has to make a living on her pension.
Literal
She [topic-は] pension [with-で] livelihood [object-を] [must-set-up-立てなければならない].
生計を立てる ('make a living,' literally 'set up a livelihood') is a stock phrase, with で marking the means of support. ~なければならない is the standard way to express obligation — 'must, have to.' Casual/spoken contractions: ~なきゃいけない, ~なきゃ.