Yup, Annie is right, there's just too much good quality protein in cat food for a dog's kidneys. But it won't hurt for a few weeks while she's rearing. (And the thing about cats and dog food is, I guess, that there's not enough good quality protein in the dog food to keep a cat healthy.)
A collie on the next door farm had a litter of 13 last year but I think that is very unusual for collies.
If your girl is struggling with making enough milk for all those hungry mouths, maybe post a question in the Dogs section? There're a lot of very experienced people on here but maybe some of them are not reading this thread.