there is no widely known or established musical group known as the "black sister of The Andrews Sisters." The Andrews Sisters were a popular American close harmony singing group from the swing and boogie-woogie eras, active from the late 1920s to the 1950s. They were composed of three Caucasian sisters: LaVerne Andrews, Maxene Andrews, and Patty Andrews.
It's possible that a new group or act emerged that gained recognition or was referred to as the "black sister" equivalent of The Andrews Sisters. However, without further information or an updated database, I cannot provide any details on such a group if it exists. If you have any specific information or context regarding this reference, feel free to share, and I'll do my best to assist you based on my knowledge .