I agree with Shiv hon - I know it must be tough, but it is just what you are used to. Taking her downstairs just gives her mixed messages/creates a new habit to break.
When R went through the 18SR it was hell. Admittedly I didn't have a new born but just managibg the hours of screamingm sleep refusal and temper was soul destroying. The only thing that got R and I through that was maintaining consistency. So, with DH taking over, let him handle her. Keep her where it is she sleeps. I promise you and DH will prevail - she will soon get the message that this is how it is to be and you will come through this, all of you. To go in to settle her for DH just gives her the message if she screams loud enough.... And then what if she does it in the night - how will you manage then hon between looking after your NB, settling her and getting no rest.
I know it's hard hon, but please hang in there. I hope that you get on ok at the docs
H x