Okay, I did everything for her to live: I met her 3 times, warned her about Kai Leng, (which happens automatically when you meet up with her via video conference in the Spectre Office), and also I gave her the Alliance resources.
I didn't romance her in 2 or 3 because my Shepard is female and, I'm sure we're friends. In my ME2 save, she was loyal and survived the Suicide mission.
I chose the paragon option when I met Henry Lawson. He let Oriana go but Miranda still dies. I also tried the exact same thing but with choosing the Renegade option at the end, to no avail.
So I went far back to my save where FemShep just finish the mission about the Catalyst and Kai Leng stole that Prothean Tech. I thought how quickly you do the Sanctuary mission affected the outcome of Miranda's life – either she dies or lives, but that didn't do anything.
So here, I searched up all the possible ways and the topics on Miranda surviving. I even went to Youtube for that and even searched for cheats but really, nothing came up. Is there something I'm missing?
Best Answer
According to the German Mass Effect Wiki you have to tell her to talk to Oriana during her Loyalty Mission in ME2. If you didn't tell her to talk to Oriana Miranda always dies in ME3.
I can't find anything about this in the English Mass Effect Wiki and can't confirm it myself right now. So it would be great if somebody can check and confirm it.