Did the discharge of Catalina for the reason given constitute national origin discrimination?

A nursing home in Iowa, whose residents were all English-speakers and all over the age of 80, instituted a rule that required that all employees speak English while working since the residents of the nursing home were elderly and not able to understand any language other than English. Several of the employees of the nursing home were Latino and spoke Spanish fluently. The nursing home informed all employees, both verbally and in writing, of the English-only rule and gave verbal and formal, written warnings to several of the Latino employees who were overheard by management speaking Spanish in the presence of residents of the nursing home. After several such warnings, the nursing home discharged Catalina for continuing to speak Spanish in the presence of residents after she had been given several warnings not to speak Spanish while she was working.

Did the discharge of Catalina for the reason given constitute national origin discrimination? Why, or why not? What factors must be considered in deciding whether an employer can legally require that only English be spoken by employees while working?