I got Rebel when he was 6 weeks old. I made sure I kept food and fresh water out at all times and made sure to watch him eat. He's never had any hypoglycemic episodes. I already had a female a little over 6 months old when I got him so I was used to yorkies.
I also gave him nutri cal twice a day and still keep it on hand just in case. He's 6 months old now and weighs 3 lbs.
I'm sure your granddaughter's puppy will be fine since you're experienced with small dogs.