Von Ahlefeldt started the new role last week, having resigned from Bell Pottinger in December 2010 and been on gardening leave since then.
Before joining Bell Pottinger, Von Ahlefeldt worked as director of healthcare at Porter Novelli and was client services director at healthcare shop, Ruder Finn.
In her new post, Von Ahlefeldt will work on business development and offer senior strategic counsel across both UK and global accounts, including the agency's business with pharma giant, Roche.
Bell Pottinger Health ceased functioning earlier this year when its parent firm, Chime Communications, funded the start-up of Open Health, the venture in partnership with former Huntsworth Health CEO, David Rowley.
As part of the start-up, life science and healthcare agency De Facto Communications, which is part of Chime, became part of Open Health. 'The big pharma side of Chime is effectively now under Open Health,' said Tristan Jarvis, associate director at De Facto.
Tudor Reilly was founded in 2007 as a healthcare agency by former BBC news reader Peter Coe and fellow broadcast journalist Julie Walters.
Managing director Walters said: 'We tried to get Tanya two and a half years ago. We're growing significantly and need senior support, and Tanya has a strong agency background.'
In February, Tudor Reilly, which moved its offering to London last year, won work with global pharmaceutical firm Sanofi-Aventis following a five-way pitch.