She will wean them when she is ready. I know another breeder who was in the same situation as you - she swore her bitch would *never* wean those pups
But, somewhere between 8 & 9 weeks they were weaned....I don't have my NR books right now but I'll look in them when I get a chance - as long as they're getting enough "real" food it should be fine.
The only other thing I can think is that if this is her first litter, she may be reluctant to wean. (Then again, the other litter was the bitch's first, too....)