Susan-Marie, depending on what you have in mind, two weeks may simply not be enough time to prepare.
If by "traditional native American songs" you mean "songs that are traditional among people who are registered members of federally recognized tribes", then many of our familiar folk songs would qualify. Some songs and hymns that have long circulated among Newcomer- or Yankee-Americans have circulated also among some Indians. As I have mentioned previously in this forum, when the new Principal Chief of the Cherokee Nation was sworn in last summer, one of the songs that was sung was "Amazing Grace" with Cherokee words.
If you mean "songs that are traditional mainly, or entirely, among those who are members of a single federally recognized tribe", then your work is likely to be more difficult. Your singers may (or may not) need to learn to pronounce an unfamiliar language and accustom themselves to an unfamiliar tonality and unfamiliar conventions of ornamentation. Also you don't want to commit any faux-pas. If your speaker is an Ojibway, you might not want to sing a Lakota war song commemorating a great military victory over the Ojibways. In fact, singing any Lakota song for an Ojibway visitor might in many (not necessarily all) circumstances be taken as a bit of "they all look alike and sound alike" ignorance.
A bit more information might be helpful. What is your visitor's ancestral tribe, and what is the topic of the talk your visitor will give ? Will the talk be a sermon on the appointed scriptures of the day ?