Her work can inhabit extreme worlds of timbre and veer off on eccentric tangents, but there is also a deep conservatism with roots in the Russian tradition of Shostakovich and the music of Bach. So much was apparent from her Composer Portrait from Miller Theatre, presented by the International Contemporary Ensemble (ICE) at the Isabella Stewart Gardner Museum on Thursday night. This group of touring New Yorkers performed four Gubaidulina works dating from between 1980 and 1993: a narrow slice of the 81-year-old’s six decade career, but nonetheless an exciting and enlightening look at her chamber music.