Isobel exists to die mainly...you could go out of your way to save her but there's not much reason to bother. I honestly wouldn't bother thinking about her that much.
She's quite important to Nightsong's story in Act 3, if you evil in act 1 she survives easy and is an interesting character to meet if a bit sudden. It's a massive leap to say she exists to die, might as well say the same about Gale or Laz, if you don't intervene they can die too.
