Christine Elsea Mandojana 

principal & founder



Christine is a U.S. Certified Public Accountant and Certified Financial Planning Professional with nearly three decades of professional experience serving in various managerial positions at “Big 4” accounting firms and in the tax, finance, and non-profit industries. 


Christine founded CEM Tax and Financial Planning in 2006 to cater to the needs of U.S. expatriates worldwide, specializing in U.S. taxation (federal and state) and financial planning.  In 2010, she co-founded Brenner & Elsea-Mandojana, LLC and continued to expand her work as a partner of this firm before branching off again in 2020 with her launch of CEM Global Tax Planning, LLC.  She has worked professionally in the U.S., Asia, Latin America and Europe, and was also an adjunct professor of accounting at the Universidad del Pacifico in Lima, Peru.  Since 2013, Christine has presented the Foreign Service Institute's annual tax seminar.  And, starting with the 2021 edition, she authors the federal tax section of the Foreign Service Journal's annual Tax Guide.  She holds a BS in Accounting, an MS in International Business Diplomacy from Georgetown University, and a certificate in personal financial planning.

As the spouse of a U.S. Foreign Service Officer, Christine currently resides in Ankara, Turkey with plans to re-locate to San Jose, Costa Rica in July 2021.

​Dina Rosenberg - Senior Associate



Sonia Alvarez-Oppus - adminIstrative assistant

Sonia AlvarezOppus Photo.jpeg

Sonia Alvarez-Oppus worked for us at Brenner & Elsea-Mandojana, LLC from 2011-2013 and is now part of our team at CEM Global Tax Planning, LLC.  She received her Bachelor of Arts degree in Political Science and Economics from University of California at Berkeley, and she has over 9 years of teaching and administrative work. Sonia is also the spouse of a U.S. Foreign Service Officer. She currently lives in Virginia.

Our Senior Associate, Dina Rosenberg, joined Brenner & Elsea-Mandojana, LLC in January 2014 and is now part of our team at CEM Global Tax Planning, LLC. Previously, she clerked in the U.S. Tax Court and worked as an attorney with the IRS and in a private-sector corporation.