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With regard to the comment on flea treatment of a pregnant bitch in the above question about worming a pregnant bitch;

Pregnant and nursing bitches can be given flea treatment using at least one product i know of Frontline spot on for dogs.
It states quite clearly on the product notes that it is safe to do so. It may not be the case in other flea treatment products but i thought I'd mention this in case anyone was unfortunate enough to suffer an infestation when a bitch has a young litter.

From what you describe you have nothing to be concerned about with your girl.
The most significant indication of the natural development of a healthy pup is weight gain. You are obviously monitoring the weight of individual puppies and the fact they are putting on weight shows she's spending enough time with them to provide sufficient nourishment for growth.

If you find that one pup is falling behind a little and not gaining as much as the others (this is more likely when a bitch spends little time with the pups as the stronger pups will always get the best teat and maybe even prevent a weaker pup from feeding) then you should ensure that the pup is given chance to feed and not be pushed out which may require you to keep the others away whilst the pup nurses.

The amount of time the bitch spends with the pups is not important what is important is the time she spends with them is helping all the pups grow sufficiently and keep them hydrated.
You can tell if a puppy is sufficiently hydrated by lightly pinching the loose skin at the scruff of the neck and releasing it; the skin should return to normal straight away.

The bitch does provide warmth for them too however if you have a heat pad or a lamp then your issue is not a factor.