
I have a small bitch like this, she even refused to give birth when she was separated from the others. I solved it by putting a large puppy pen around the whelping box so that she was both on her own and not at the same time.
My large bitches would kill any of the other large dogs if they were near them during the last few weeks of pregnancy, the birth and the first few weeks. There is no way on earth they would accept their normal friends. But interestingly, when I have large pups, after only a couple of days I usually find both toydogs and cats sharing the whelping box with the mother, all perfectly happy! It's like they don't count. My 3 kg toy bitch helped my 22 kg large bitch rear her pups last time (she washed them, played with them when older etc), and continued to treat them like her own pups until they were many times her own size. Mum was quite happy to have a baby sitter!