Istee is a partner in the Tax, Trade and Wealth Management Practice Group of Wong & Partners. Her key practice areas are Malaysian tax planning and advisory work, including areas such as income tax, real property gains tax, stamp duty and indirect tax. Her practice also extends to corporate compliance and issues relating to investments and setting up of operations in Malaysia across multiple industries. She also manages corporate exercises, including cross border mergers and acquisitions. She is also experienced in matters involving restructurings, and post-acquisition integrations.

She also has a core focus on wealth management and succession planning and she is a full member of Society of Trust and Estate Practitioners (STEP). Istee's practice focuses on advising high-net worth individuals, financial institutions and intermediaries on the legal, regulatory and tax issues in setting up a succession planning structure. She has also assisted families and individuals with the actual implementation of such structures, which includes the setting up of Malaysian or offshore trust structures. Her Wealth Management practice was named the Tax and Trusts Law Firm of the Year by the Asian Legal Business Malaysia Law Awards in both 2020 and 2021, and is ranked as a Band 1 practice by the Chambers High Net Worth Guide for Private Wealth Law.

Istee has collaborated on several guides and publications. Her most recent contribution was to the Society of Trust and Estate Practitioners (STEP) and in the STEP Journal Issue 5, 2022, she co-authored an article titled "Course Correction" which discusses Labuan's adoption of international taxation standards. In addition, she has contributed to the LexisNexis Practical Guidance – Tax, in which she co-authored the Taxation in Malaysia: Overview, Taxation of Trustees and Trust Funds, Automatic Exchange of Information and Succession Laws in Malaysia articles.