Welcome to YT!
8 weeks is pretty young - most breeders will not let yorkies go until they are at least 12 weeks old. So, your baby is quite vulnerable to a lot of things, including hypoglycemia - which is common to yorkie pups - do you have Nutrical at home?
How long has she had the runs, what is the parasite and what med is she on? Having diarrhea can put a puppy in an emergency situation in a flash - so if she's had it for more than a day or so, she may need to get back into the vet or she'll probably dehydrate and need to get on IVs, which is good to avoid.
As for food, I'd be feeding about 4x per day at her age. How is her appetite and drinking? Are her gums pink?
Lastly, it's pretty common for a 3 year old child
not to understand how fragile a puppy truly is, you're not alone there. So, I'd just make sure the puppy is always supervised.