*Spoilers about a mission near the end of Mass Effect 3 will follow*The other guide is right for mentioning the Sanctuary mission on Horizon, the completion of which grants you this achievement. However, something happens at the end of this mission, which I think should be of value here. Don't want to know what happens? Don't open the spoilered text!
*** Spoiler - click to reveal ***So at the end of the mission, Miranda could die. I wanted to know when she dies and when she lives, and I've found the following information about the aftermath of the mission. I copied it from the Mass Effect wiki and I take zero credit for writing it; however I've found it backed by enough sites to know it's valid.
There are multiple potential outcomes:
If you ask about Henry Lawson's legacy, the camera will focus on the cracked glass behind him.
If you can't pass the Reputation check and "just want Oriana", you'll have a Renegade Interrupt option to wound her in the leg, distracting Henry:
If Miranda is present, she will slay her father via biotics and Oriana lives.
If Miranda is not present, Shepard can kill Henry with another Renegade Interrupt. Otherwise, Shepard will tell Henry to run away, letting him go.
If you don't take the Renegade Interrupt and Miranda is not present, Oriana will backpedal towards the glass and throw herself and her father down, which ends in both of them dying. If Miranda is present, she'll kill her father, but her father will also mortally wound her.
If you do pass the Reputation check, you'll be able to use a Charm/Intimidate option that gets Henry to release Oriana. If so, you'll get a Renegade option that allows you to kill him. If Miranda's present, she'll take it before you get a chance to.
If Miranda is present, the following conditions will determine whether she dies.
If Miranda wasn't warned about Kai Leng, or if you didn't complete her Loyalty Mission, she'll be gravely injured and die at the end. Warning about Kai Leng requires reading the dossier on the assassin before speaking to Miranda over vidcomm, and completing her Loyalty Mission means you must have at least imported a Mass Effect 2 save.
If you break off a romance with her she will also die, regardless of whether you did both her loyalty mission and warned her of Kai Leng.
If you deny her access to Alliance resources during your third meeting, or if you never met for the third time on the Citadel, she will die.
Note: Miranda may appear wounded in the cut scene, but can still survive.