Trivia: Among the girls at the slumber party are Florence Henderson's daughter Barbara ("Ruthie") and Robert Reed's daughter Carolyn ("Karen"). They interact briefly; during the game of Truth Or Dare, Ruthie is dared to go check on the boys and asks Karen to go with her. In addition, Hope Sherwood ("Jenny") is the daughter of executive producer Sherwood Schwartz.
Trivia: In Season 2, out of the five episodes with one of the kids not appearing in the entire episode, three episodes used the name of the missing kid in the dialog most likely to make their absence from the episode more unnoticed. (Marcia/Peter/Bobby in these cases - each one's name mentioned at least once even though they never appeared). The episodes were ("What Goes Up...", "The Tattletale" and "Coming-Out Party"). Also the 4th episode of season 2 - "A Fistful of Reasons" contained Jan being mentioned yet she did not appear in the entire episode.
Answer: The dangling bracelet was used for dramatic purposes - to keep the audience on edge.