Someone PLEASE SPOIL ITTTT FOR MEEEE ヽ(`Д´)ノ
Spoiler! (Though its been a long time since I read the novel and I only remember the major scenes and not everything is in the exact timeline because so many things happen at the same time.)
Mielle and Oskars sister will try to set up aria on various occasions though she will always somehow turn it in her favour. Our lovely Asher is indeed the crown prince (as many have probably guessed) and he and Aria will become the most adorable scheming couple. Aria becomes renowned as investor A and has a lot of businesses that flourish under her.
At some point Mielles older brother will become more and more obsessed with aria thus going so far that he will try anything to keep her by his side. To separate the prince and aria, the Roscente siblings throw their own father down the stairs and blame aria but she escapes thanks to Ashers special ability (some kind of teleportation) and because they move far away they mange to get a waterproof alibi. In the end they will turn the story around so that Mielle is under house arrest for taking drugs (because she said aria was at the crime scene and just vanished (Asher))and the father survives but is now a cripple.
Mielles brother has to take over the position as family head but at the same time he supports anti imperials and gets caught and thrown into prison.
Mielle and Oscar's sister flee to a neighbourhood country and try to get rid of asher with that king, but they get played the whole time because Asher and that king are actually good childhood friends. So Mielle and the Frederick's are sent to prison and all of the Frederick's get executed. (Except for Oscar because he was against his familys plan and helped asher)
Aria pretends to save her sister who will than be bound to annie (she can't leave her side or she'll be killed) who greatly humiliates Mielle on arias order. Aria pretends to be nice to Mielle and makes her believe that Aria is actually a pure and good person and than told mielle to drug (poison) Annie as a prank. Mielle ends up poisoning her own brother through Arias schemes and will then be executed.
Their Father killed himself after these news and Aria is finally free enough to live a happy live with Asher.
That was just some points there is a lot else going on such as all the schemes, Annie's and count bourbons and Jessie's and Hans love story, how Aria helps her mother to scheme the crippled count roscente of his money while leaving him (heart-)broken and alone in exile, Arias and Ashers lovestory <3 etc, etc ...
Fuck me(╯°Д °)╯╧╧