Complex sentence: Ono is often associated with the Fluxus group, whose founder George Maciunas, her friend during the 1960s, admired and promoted her work enthusiastically, giving Ono her US show at his AG Gallery in 1961.
Split into simpler sentences: Ono is often associated with the Fluxus group, whose founder George Maciunas was her friend during the 1960s. Maciunas admired and promoted her work enthusiastically and gave Ono her U.S. show at his AG Gallery in 1961.