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Isabel F. Thelen

Portrait of Isabel F. Thelen

Isabel is a member of the firm's Professional Liability Department where she focuses her practice on the defense of a broad range of clients including attorneys, accountants, insurance producers, corporate directors and officers, and financial institutions.  She has experience handling all stages of litigation, from pleadings and motion practice to discovery and settlement negotiations and has represented clients in complex commercial disputes, including actions in federal court as well as administrative proceedings.

Prior to joining Marshall Dennehey, Isabel worked as an associate at a New York law firm specializing in civil litigation, among other areas. She has also completed multiple legal internships and collaborated closely with attorneys during trial preparation in these roles.

Further, Isabel gained valuable litigation experience as a student attorney at the Glushko-Samuelson Intellectual Property Law Clinic of the American University Washington College of Law where she obtained her juris doctor degree. During law school, Isabel served as Associate Managing Editor for the American University Business Law Review. She holds a Bachelor of Arts degree in Global Commerce with a minor in Economics from Denison University. 

Isabel is admitted to practice in the state of New York.  Outside of work, she enjoys cooking, reading and listening to live music.

    • American University Washington College of Law (J.D., 2024)
    • Denison University (B.A., 2021)
    • New York, 2025
    • U.S. District Court Southern District of New York, 2025
    • U.S. District Court Eastern District of New York, 2025
    • New York State Bar Association

Firm Highlights

Thought Leadership

Appellate Division Affirms Dismissal of Legal Malpractice Counterclaim Against Martin Law Firm

In Martin v. Loury, 2026 N.J. Super. Unpub. LEXIS 1617 (App. Div. July 15, 2026), Martin Law Firm represented Kirk Loury in an employment matter Mr. Loury filed against his former employer, Concord Equity Group Advisors LLC (“Concord”). The allegations included, among other things, that Loury was not fairly compensated for his employment with Concord. After a bench trial finding in Loury’s favor, the Appellate Division remanded this matter in February 2016 for a second trial. During the second trial, Concord CEO, Lee Argush, testified to lower compensation estimate than first trial. On remand, the second trial judge awarded Mr. Loury the same damages as the first judge, finding Mr. Argush not credible. After the findings during the second trial, Martin Law Firm filed an action against Mr. Loury to recover legal fees and costs of representing Mr. Loury in a second bench trial and Mr. Loury filed a counterclaim against Martin Law Firm for legal malpractice, alleging he should have received an even higher award in the second bench trial. In this allegation, Mr. Loury, through his expert, claimed that Martin Law Firm should have recalled Mr. Loury to the stand to rebut Mr. Argush’s testimony to allege an alternative theory of damages. Mr. Loury’s expert admitted that the second judge already rejected Mr. Argush's theory and accepted Loury's damages theory. The trial court barred Mr. Loury’s expert and dismissed Loury's counterclaim with prejudice before convening the collection trial, and the jury ruled in Martin Law Firm’s favor. Mr. Loury appealed the trial court's pretrial rulings barring his liability expert from testifying in support of his legal malpractice counterclaim, denying his motion for summary judgment on that counterclaim, and denying his motion to amend his counterclaim by adding attorney Joseph A. Martin as a codefendant. In affirming the trial court’s decision, the Appellate Division held that the trial court properly excluded Loury’s expert testimony in the counterclaim against Martin Law Firm because the expert could not explain how calling Loury as a rebuttal witness would have increased damages when the second judge already rejected Mr. Argush's testimony and accepted Loury's damages theory, making the expert’s causation opinion speculative. The Appellate Division also held that the trial court properly denied Mr. Loury's summary judgment motion on his malpractice counterclaim because reasonable minds could differ on whether Mr. Martin's alleged failures would have changed the second judge's damages award, given the judge already found Mr. Argush not credible, creating genuine factual disputes precluding summary judgment. Also, the Appellate Division held that the trial court properly denied Loury's May 2023 motion to add Joseph Martin individually because the statute of limitations expired in February 2022, six years after the 2016 appellate remand when Mr. Loury incurred new legal costs, and relation back did not apply because Mr. Loury knew Mr. Martin's identity throughout and strategically chose to sue only Martin Law Firm in his 2019 counterclaim.