as gestational age
increases the demands of the baby also increases, so your wife should take diet not only for her for her baby also.
Every pregnant woman should take iron, folic acid
tablets and calcium tablets along with good nutritious diet.
You didn't mentioned her treatment history, if she is already taking above medicines you encourage her to take good diet and little exercise like walking in the morning and evening for around 20 to 30 min.
Investigations like hemoglobin
, blood pressure, blood sugar etc should be done and if any abnormality detected she has to be treated according to that.
And most of all you and other family members should give moral support to her and enquire whether she is worried about process of delivery. If so, let your gynecologist council her.