I'm not sure if this is a glitch, but as of writing, Angela doesn't actually have to live to the end for this to pop. On my first playthrough, I got Angela all the way to the burned house in the "Heavy Burden" second-to-last chapter. When she and John are approached by their demons outside, you're presented with a choice for Angela between Resentful "I'm not waiting for you" or Reassuring "Please hurry!" Make sure you select the Reassuring "Please hurry" option, and (for me at least) the achievement popped immediately after that.
*** Spoiler - click to reveal ***Then I missed one of her QTEs and when John is presented with the option to help her or run away, I chose run, and Angela was killed. I think the key to these "saved (character)" achievements is for them to be selfless and tell the others to save themselves/go on without them whenever you have that option. Passing all of the QTEs and actually keeping them alive doesn't appear to be the deciding factor.