oh yes, tsw. i agree. Olenna is perhaps the most skilled player of the Game in Westeros. And Margaery is her star pupil.
The Queen of Thorns can be credited with making House Tyrell the single most powerful in all of Westeros. They currently hold the balance of power, emerged unscathed despite backing Aerys in Roberts Rebellion, They've supported three (and married Margaery to all three) kings so far, and have accumulated ever-more power in the trade-ups.
Olenna is quite critical of Mace's mental and politcal accumen, and its clear that he would do practically anything she advised him to do... not many people are capable of saying no their mother, when she has certainly raised them to always acquiesce to her will.
Margaery is a junior, but talented player, and no doubt is in on most of Olenna's plans - especially in her own role to play.
Both seem well aware that public opinion and provable fact are essential in manipulating the game. Hence Olenna's insistence on Tommen and Margaery sharing a bed on the night of their wedding.
I never thought of Margaery as being either a lesbian, bisexual or bi-curious even. Real World history does tell us that many high born ladies had their ladies in waiting share their rooms and even their beds, as surety of virginal integrity.
Cercei is a rather disturbed woman. Whether she was comparing her own bisexuality to Margaerys, or to Margaery's possible incestuous relationship with Loras (whose homosexuality is not just hinted at...but rather blatantly revealed in a couple of locations), has no bearing on Margaery's "reality".
I feel a little sorry that Sansa was unable to stay as part of Margaery's court, she could have received training in the game from a far more gifted source than Littlefinger... who whilst being a good player, isn't a woman, and therefore cannot teach Sansa of her feminine power and how to wield it as the power beside the throne (rather than Littlefingers power solely from the gold). As Olenna definitely could have done.