Complex sentence: Stuart worked at the Freer and Sackler Galleries for more than 20 years (1988-2006), before taking the position of Keeper of the Department of Asia at the British Museum (2006-2014).
Split into simpler sentences: Stuart worked at the Freer and Sackler Galleries for more than 20 years (1988-2006). She then took the position of Keeper of the Department of Asia at the British Museum (2006-2014).