My wife is undergoing chemotheraphy. Is it normal for her to get nauseated after five days of therapy?

Depends. The type of therapy and how an individual responds to that therapy both impact the degree and timing of nausea. What you are describing is delayed nausea and this is treated a little differently than nausea around the 1st 24-48 hours of treatment. Make sure your health care provider is aware of this because they will probably add a different anti-emetic regimen to reduce this side-effect.
Delayed nausea. It is not unusual for people to get delayed nausea from chemotherapy. Is she taking nausea medication? She should discuss this with her oncologist who may prescribe additional medications to help with the nausea.
Chemotherapy Nausea. Yes some of the chemotherapy drugs such as cisplatinum have nausea and vomiting lasted for several days.