“This is my sister, celebrate her with strings" comes from the play The Glass Menagerie by Tennessee Williams and is set in 1937 in pre-war America. The play focuses on the dysfunctional family life of the Wingfield family. Amanda Wingfield is one of the primary characters within this play and is described as a fading southern belle who yearns for the comforts of her youth. Her husband has abandoned her and she is struggling financially to raise their children on her own.
In scene six Amanda is assisting her daughter Laura with getting ready for a date with a suitor. During this interaction Laura does not wish to wear the accessories that she feels falsify her beauty as she feels like she may be setting a false trap for the suitor to which Amanda replies that men expect pretty girls to be a trap. Within the script you see “legend” this refers to a screen present within the play on which images or titles are presented. This is similar to the subtitles within silent movies. Within scene six during the conversation between Amanda and Laura the legend states “This is my sister, celebrate her with strings” is intended to invoke sympathy for Laura and change the tone onstage as Laura moved from being unsure to being upbeat about meeting her suitor and being exciting about how she looks.