ACC- Erica is a citizen of a foreign country

Erica is a citizen of a foreign country, and is employed by a foreign-based computer manufacturer. Erica’s job is to provide technical assistance to customers who purchase the company’s mainframe computers. Many of Erica’s customers are located in the United States. As a consequence, Erica consistently spends about 100 working days per year in the United States. In addition, Erica spends about 20 vacation days per year in Las Vegas, since she loves to gamble and also enjoys the desert climate. Erica does not possess a green card. Assume that the United States has entered into an income tax treaty with Erica’s home country that is identical to the United States Model Income Tax Convention of November 15, 2006.

How does the United States tax Erica’s activities? How would your answer change if Erica were a self-employed technician rather than an employee?