If you had tried to bottle feed it, it probably would not have survived anyways. To keep it warm, you could have brought the mom, baby inside, but considering how many problems your doe has had with this litter, I am not entirely surprised that she lost her living kits too. When she was with the buck for breeding, did you just bring the buck to her for breeding, or were they in a cage together for a while, like a period of days? I am wondering if she had been pregnant with 2 litters a few days apart, as can happen if a doe is re-bred while pregnant.