Is Margaery accused of anything beyond bearing false witness?

Question

During the trial of her brother Loras, Margaery lied. As a result, she was arrested. If Margaery confesses and does a "Walk of Atonement", she will be let out of the dungeon. But she still faces a trial for something.

Only confessing to adultery with Lancel Lannister and a "Walk of Atonement" was enough to get Cersei out of the dungeon. But she still will justifiably be put on trial for murder, more incest, treason, etc.

Confessing to lying during a trial and a "Walk of Atonement" will get Margaery released from the dungeon. But then, what is Margaery to be put on trial for?

Has Cersei cooked up some false charges against Margaery and told the High Sparrow? Or am I not remembering something?

Answer 1

Yes.

In the books, Cersei has Margaery accused of fornication with Osney Kettleblack and a wide array of other supposed lovers. From the aSoIaF wiki:

Cersei accuses Margaery of adultery and treason, lining up an impressive, if untrue, array of conspirators and evidence by torturing the Blue Bard. After Cersei discounts accusing Loras Tyrell, Horas Redwyne, and Hobber Redwyne, Maergery is accused of having slept with:

• Osney Kettleblack
• Jalabhar Xho
• Bayard Norcross
• Ser Tallad the Tall
• Hugh Clifton
• Hamish the Harper
• Lambert Turnberry
• Mark Mullendore
• The Blue Bard

Margaery is arrested and imprisoned to await trial by the Faith at the Great Sept of Baelor. While in custody, Margaery confronts Cersei, revealing that she knows that Tommen's mother is behind the accusations and wants to remove the young queen from a position of influence, perhaps by arranging for her death. Later, one of Cersei's key witnesses, Osney Kettleblack, reveals her plots under torture, and Cersei soon finds herself sharing Margaery's plight under similar charges.

For more details, see A Feast For Crows, Chapter 39.

Answer 2

No

As per the show she isn't accused of anything else; rather that she will stand trial to find out if she is guilty of anything else.

CERSEI: Her accommodations seem sufficient. What happens to her now?
SPARROW: Well she and her brother are both being held under fair suspicion. A trial will be held for each of them to determine if they are guilty of any acts that might constitute a violation of the tenants of the faith.
_{Game of Throne, Season 5 Episode 7, "The Gift"}

Later in the episode we find out that if one of them should confess before the trial then they won't need to face it but will instead be at the Mother's mercy.

CERSEI: If one or both of them were to confess before the trial…
SPARROW: Then they will be at The Mother’s mercy.
CERSEI: What does The Mother’s mercy entail?
SPARROW: It depends on the situation. The acts themselves, the degree of contrition.
_{Game of Throne, Season 5 Episode 7, "The Gift"}

Later on when Margaery is in her cell the High Sparrow visits her and they have the following conversation:

HIGH SPARROW: It isn’t Ser Loras that brings me here. Your husband misses you dearly. The love between a man and wife is sacred. It reflects the love the gods have for all of us. But sin leads us away from the sacred. And only confession can purge sin.
MARGAERY: I have nothing to confess.
HIGH SPARROW: So you believe you are pure? Perfect? Wholly without sin?
MARGAERY: None of us are.
HIGH SPARROW: You have started down the path. But you have many miles to go..
_{Game of Thrones, Season 6 Episode 1, "The Red Woman"}

So she is commenting that she isn't wholly free of sin and the High Sparrow seems to accept that as her starting on the road to redemption.

It's never fully stated if she confesses or not but she does start to believe, or pretend to, in the ways of the High Sparrow. She even goes as far as convincing Tommen to convert.

TOMMEN: What about Loras?
MARGAERY: I love my brother. I will always love my brother. His soul is pure and perfect. His sins don’t erase that purity, they only obscure it. He just needs to atone for them. We all do. Sooner or later, one way or another. The gods have a plan for us all.
_{Game of Thrones, Season 6 Episode 6, "Blood of My Blood"}

The above quote doesn't exactly show that she has converted Tommen but that she is now acting in the ways of the Faith. However, later on in the episode when Jaime comes to stop the Queen from her walk of atonement we have the following scene. It's unclear if Margaery confessed to anything for the walk or if it was for show to stage what happens.

HIGH SPARROW: To die in the service of the gods would please each and every one of us. We yearn for it. But there is no call for it today. There will be no walk of atonement.
CAPTAIN: Order up!
HIGH SPARROW: Queen Margaery has already atoned for her sins by bringing another into the true light of the Seven. Together we announce a new age of harmony. A holy alliance between the Crown and the Faith.
WOMAN: Long live King Tommen and bless you, Queen Margaery!
TOMMEN: The crown and the faith are the twin pillars upon which the world rests. Together we will restore the Seven Kingdoms to glory.
_{Game of Thrones, Season 6 Episode 6, "Blood of My Blood"}