A/N: Since I didn't really explain the events surrounding the Red Wedding and how the MC being allied to them changed, something's here is a little more information.
Jaime Lannister, who was still a captive of the Stark's was freed after the events of the Red Wedding. House Bolton was bought by Tywin Lannister to free his son Jamie and kill the Stark's during the wedding, and in return House Bolton will be named Warden of the North.
In Canon, the Red Wedding happened because of Robb breaking off the marriage between him and Walder Frey's Daughter, which angered Lord Walder Frey greatly. And in response Lord Walder Frey secretly begins corresponding with Lord Roose Bolton, who has wed Walder's granddaughter Walda, and Lord Tywin Lannister for terms to bring House Frey back as a supporter of the Iron Throne.
This worked in Tywin Lannister's favor, as now he could rescue his son and deal with the threat in the North at the same time.
Normally, Jamie would have been freed by Catelyn Stark in exchange for her two daughters Sansa and Arya, but because of Maximus support and claim that he can rescue them, Catelyn refrains from releasing Jaime Lannister and instead keeps him as a captive.
And since Jamie wasn't freed, then that means he wasn't being escorted back to Kingslanding by Brienne of Tarth, so his hand wasn't cut off. Brienne of Tarth continued to serve Catelyn Stark as her Knight and unfortunately died at the Red Wedding when House Stark was ambushed and killed.
A/N: Now that I explained it a little more, the next part is the actual chapter
After arriving at Highgarden Aerella and Aleanna were greeted by Olenna Tyrell who had already known that she was coming to meet with her so Aerella was allowed inside the castle where she met with Olenna. Aleanna stayed outside with the guards.
Aerella and Olenna had sat down in a room with where they first talked about the various things that were going on in the world, with Olenna asking something's about the Empire and how life is there. After a few minutes of talking about that, the real discussion had started.
"So Lady Olenna I know that Margaery is betrothed to King Joffrey, and she wishes to be a queen, but I think there is a better suitor for your Granddaughter" Said Aerella
"And are you going to tell me that the Emperor is a better suitor for her, hmm" Said Olenna
"It seems you have read my mind, since that is exactly what I was going to say, but it's not just because of Margaery" Said Aerella
"The Tyrell's have a lot of influence in Westeros and has the best land which would be useful for us once we land in Westeros" Said Aerella
"Are you telling me somebody that you don't even know that you are going to invade Westeros, which could backfire on you if I tell King Joffrey" Said Olenna
"You call him King Joffrey when he is not even the true King of the Seven Kingdoms" Said Aerella "We have evidence that he is not Robert's son but is instead...."
"The son of Jamie Lannister" said Olenna "Yes we have heard of this rumor going around but not many people believed it so are you telling me that you have evidence" Asked Olenna
"Yes we have evidence, in fact I have it with me" Said Aerella as she reached her hand up near her shoulder and a Shadow Guard placed a book in her hand. Olenna was shocked, but she didn't show it on her face
"This will give you the evidence right here" Said Aerella as she turned to the page where it showed Lineage's of the Houses of the Seven Kingdoms. She turned to the page of the Baratheon lineage and showed Olenna how every Baratheon born had black hair and then turned to the page of Joffrey who had Golden Hair.
Olenna was stunned at how she didn't notice this, "So the Rumors were true then Joffrey is not even of Baratheon blood but is instead the offspring of Jaime Lannister and Cersei Lannister"
"It is as you see the Lannister are growing powerful every day and with King Joffrey on the Throne they would be able to control Westeros for centuries to come unless we stop them" Said Aerella
"Though even if you don't accept the deal his majesty's army is unstoppable and with two dragons at the head of this unstoppable army Westeros will fall in due time" Said Aerella
"If he has such a thing then why does he need to make an alliance with House Tyrell then" Asked Olenna
"Because his majesty doesn't want to just conquer the entire Continent since even if he has a large army the amount of people that will dislike him will be a lot and plus his majesty doesn't want to deal with fighting a war against most of Westeros" Said Aerella
"And a couple of little birdies told me that Joffrey is very abusive towards his Sansa, even using his Kingsguard to strike her and torment her everyday with having her father's head on a pike in the Castle" Said Aerella
Olenna didn't want her daughter to be treated like Sansa and if her Hot-tempered Grandson Ser Loras saw his sister getting mistreated, he would kill the King, and she didn't want Loras to become a Kingslayer.
But at the same time she didn't know the true intentions of the Empire since if they do invade Westeros as Aerella says then what are they aiming for The iron Throne or something else.
"My son always dreamed of his daughter marrying a King, and now she is almost close, but the King in question is not fit for her" Said Olenna
"Why does the Emperor want to marry Margaery anyway, besides getting an alliance with is" Asked Olenna
"Actually, his majesty doesn't know about it, he only allowed me to go on this trip so that I could meet with you for an Alliance but how I will get the Alliance he doesn't know" Said Aerella
"You have that much power that you can do that" Said Olenna since she was surprised a woman had such power
"Women must be treated differently over there than from what I heard" Said Olenna
"Yes, Women are treated differently, but we are actually special since we are also betrothed to his majesty" Said Aerella as she was referring to Aleanna
"You mean that you and that other girl are betrothed to the Emperor" Asked Olenna
"Yep" Said Aerella
"Then how would my Granddaughter fit into the picture when he already has two wives" Said Olenna who wasn't happy hearing about this
"Well he actually has three but besides that we would all become Queens once we marry him and not only that we would all be sisters and nobody will have more power than the other nor will anybody try and kill each other since that is punishable by death" Said Aerella
"I don't know, even though it is a good deal I still need time to think about it since this would be a big decision" Said Olenna
"I understand Lady Olenna so if you would excuse me I have to return to Essos since If I don't then his Majesty will come here with an army" Said Aerella as she chuckled
"But once you make a decision, please let me know immediately since time is of the essence and who knows what will happen in the coming months" said Aerella as she left Olenna to think about what to do.
Though one thing was for certain, that she wouldn't let her Granddaughter marry King Joffrey.