I think a pup that young is going to need to be on a milk replacer, in conjunction with puppy food- a regular puppy food on its own wouldn't have enough fat or protein or minerals for her. In two more weeks maybe...but giving her a milk replacer now could make a big difference in her longterm health.
I haven't fostered any puppies yet, but a LOT of kittens.
If you can't get puppy formula, then you can use whole goat's milk. You'd need to skim some of it, and add the fat back to some whole goat's milk. Keep the skim for yourself, and use the extra fattened for the pup. Dogs and cats both have fattier milk than goats, I know that. But goats have very small easily digested proteins in their milk so a lot of other animals take to it well. (steer CLEAR of cows milk)
She should be ok to lap the milk at her age, and not need a bottle. While it may be tempting and fun to offer a bottle, it won't help her at all to learn proper eating, now that she's old enough to lap. (I have a cat who I let stay on a bottle too long and be darned, at 7 years of age, he still has trouble picking up kibbles, and will 'suck' soft food as opposed to licking it)
I would think its ok to completely bathe her, if you do it in a warm room, and do it quick. Then wrap her up and keep her snuggled against you, changing to a new dry towel every so often, til she's dry. I do this with kittens, they get messy from eating and when they poop, and its important to keep them clean so they will grow accustomed to being clean, and be a clean adult in turn. If you don't keep them clean as babies...they sometimes don't end up cleaning themselves as an adult. The breeder or puppy broker likely gave you that advice in good conscience based on their experience that if they bathe pups and put them back in a cage, they all catch a chill and get sick. Its the snuggling part that is key.
I know its also good to keep them with you as much as possible- as in inside a baby sling or carrier, against your body. Put her down to exercise when she's awake...but let her sleep on you or your friend. She's an orphan and you need to take the place of her mom-baby dogs and cats need to be snuggled against other animals pretty much all the time until they're 7 or 8 weeks. Its not just about warmth, its about the brain secreting the feel good hormones and chemicals that lead to proper brain development and normal functional personalities. Humans are the same way, but we just take that for granted.
If you can, find someone else who has pups near the same age, if you can socialize her with other pups at least every day...I'm sure it will help a lot. I'd be very concerned about her personality development if I were you. My last dog was a rescue, who came from a dog farm originally. He was really sweet, but also had a terrible mean side, which inevitably put my family at danger. Even if you can regularly socialize her with a gentle adult dog, it would be better than nothing. I can't stress this enough. Even with cats, the ones I fostered that were singletons, when I had no other cats....they turned out to be weird adults. Not such a big deal with a cat, but with a dog, that could jeopordize your safety. Ideally, you would have a calm gentle adult animal of the same species in the house before fostering an orphan.
Hopefully a breeder on here can confirm this thought too- A pup of 5 weeks may not normally poop on their own yet when they're with their mothers. Mother cats stimulate the kittens to defecate and urinate by licking their genitals until they're 6 weeks. Yes, they do begin going on their own at 4 weeks, but the mothers still do it sometimes for them at that age. I don't know 100% but I think mother dogs do clean their bums for as long or longer than a cat does. Its really important, even if she goes on her own most of the time to still do this, if that's the case, otherwise she might be setting up for bowel problems as an adult. You basically just take a warm moist washcloth, and wipe the genitals gently from front to back, and 'it' comes out. Then you put a little vaseline on after to keep the skin soft (the mother would use her saliva
).
Having a very young animal is and should be a LOT of work. You can choose not to put in that amount of time, but the results may not be too good in the long run.
The good part is, the hard work only lasts for a few weeks. In 3 weeks, she'll be just like anyone else's pup...just maybe need a little more socialization.
Congrats on your new baby and best of luck, hope my info helps!!!