Cynthia Robinson, trumpeter and founding member of Sly and the Family Stone

Girls don't play trumpet, they told her.

Cynthia Robinson had an answer to that — one that would later resonate in the hit song she recorded with Sly and the Family Stone: "Thank You (Falettinme Be Mice Elf Again)."

More than any other lyric coined by the iconic hippie-funk band of the 1960s, that's...