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​Sumin Im - Tax Associate

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Sumin Im is a licensed CPA in Virginia. Prior to joining CEM Global Tax Planning, LLC, she worked in global banks and private equity firms for over 10 years. She has her BA in English Language and Literature and BS in Political Science from Sookmyung Women’s University in Seoul, Korea. Sumin is the spouse of a U.S. Foreign Service Officer and is currently located at Berlin, Germany. 

​Katrina Arpaia - Tax Associate
MS Taxation 

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Katrina Arpaia has 10 years of previous tax experience in public accounting and industry. In her managerial positions at a Big 4 firm and corporate headquarters, she enjoyed helping others through mentorship, coaching, and teaching opportunities. Katrina holds a BS in Business Administration with a concentration in Public Accounting, an MS in Taxation, and is currently pursuing the Personal Financial Specialist credential. She is a member of the American Institute of CPAs, Financial Planning Association, and Financial Therapy Association.  She currently resides in the U.S.

Sonia Alvarez-Oppus - adminIstrative assistant

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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.

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 Arlington, VA.

​Dina Rosenberg - Senior Associate



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. She currently resides in the U.S.

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