I dont think you need the drs approval - just that if they flag up any medical ishoos they need to inform the dr. I already had drs go ahead to do low calorie as I'd spoken to him about (between me and you) wanting to try prescription diet pills and he advised me to try CD or similiar instead.
Just wear what you're comfy in because she will want to measure you too (this includes THIGHS - horror of horrors!!) and then wear similiar clothes each week to get re-weighed.
I found soups pretty awful but you might like them - I suppose give them a try but dont get loads of sachets of them just in case.
Dont forget you need a blender!!