She became a partner of Marijke Klinkhamer in 2002 and took over Artists Management Klinkhamer van der Vliet in January 2005. In 2006 the agency, with Stephan Brekelmans as a new partner, took over Interartists Amsterdam from owner Janine Salomons. With this takeover, the activities were expanded from Benelux management to international management.
Besides her studies of musicology Leontien studied cultural policy. She was a member of the editorial staff of music journal Mens & Melodie as well as radio broadcast company ConcertZender. At the ConcertZender she co-operated with several composers on the subject of integration of authentic non-western music in their compositions. In 1992 she founded the Cultural Institute for Development Taiwan, together with the composers Wen Loong-Hsing and Sebastiaan Jansen, for the purpose of touring Taiwanese cultural groups in the Netherlands. She was also an active violinist in various chamber music groups within the university. Her interests include literature and rowing.