Poor lamb, poor you as well. Honestly, just do whatever you need to op. I'd probably just let her sleep in your bed if that is what helps. Encourage her to start the night in her own bed but just reassure her that if she gets scared, you're always there and won't turn her away. A few weeks of that and she may regain some confidence/faith in the whole situation, become more secure that new baby hasn't completely usurped her, and hopefully go back to her own bed.
I personally don't see the point of trying to get them to sleep alone if they're scared.
My own ds night terrors seem to improve if I make sure to tell him each night that I will take care of him if he sleepwalks, that I'll be there and make sure he is safe, that I always love to see him even in the middle of the night (!!).
It is awful op, I know you're exhausted. I sympathize hugely.
My personal experience has taught me that allowing the fears to happen and to be the secure comforting presence (not over discussing it with them, not getting worked up, just plodding through the night dramas at their side) seems to neutralize the issues quicker than trying to strategise/explain etc.
Regardless, my heart goes out to you, its really hard.