Cher Horowitz is a closeted lesbian.
Cher expresses explicit distaste in boys her age on more than one occasion, and is disgusted by the idea of dating one. She focuses her attention of unattainable men, like Luke Perry and her gay classmate Christian, and uses having high standards as an excuse for not seeking a boyfriend. The reason Cher becomes jealous when Tai shows interest in Josh is because she has developed feelings for Tai, which Cher fails to recognize. Cher projects her feelings for Tai onto Josh because it's easier for her to buy into compulsory heterosexuality than to come to terms with her sexuality. Miss Geist deliberately threw her bridal bouquet to Cher
Miss Geist is facing forward when she makes the toss, and if you watch the bouquet toss carefully, the bouquet lands directly in Cher's hands, but before she can close her grip she gets jostled and has to fight for it. Miss Geist probably didn't make Cher a bridesmaid just for hosting the wedding and reception at her house (though it's a heck of a favor); Miss Geist is portrayed as absent-minded but quite clever, it's possible that she realized that Cher was instrumental in sparking her romance (though probably not the reason why!) and wanted to acknowledge/repay her in some small way. She definitely looks satisfied when Cher stands up triumphantly brandishing the bouquet!