She has been asked to grow the client service team through organic business development and growth strategies.
The agency said Alder-Shah will bring "a deep-rooted understanding of client business and driving excellence in creativity through innovation".
She reports to Ete Davies, managing director.
Alder-Shah joined Dare in 2012. There she led the client teams to work on digital comms, user experience, design, platform and service design for clients such as Experian, Unilever and Barclays.
Davies said: "Not only is [Alder-Shah] a great cultural fit, her experience both agency side at Dare and client side at Barclays, combined with her unique set of skills, brings a sense of completeness to AF's current offering and an incredible platform towards our future ambitions."