Speaking as someone who was a vet tech for many years, who showed dogs, and made a living training dogs, when that many puppies are involved there is still very seldom any reason to supplement puppy feedings. So your “wait and watch” plan is a solid one. Being prepared is also smart. But don’t interfere unless you have to ~ nursing them forms a solid bond with Mom and the pups need that early colostrum, which milk supplements don’t provide.
I would suggest giving her some cottage cheese for a few days. She’ll love you for it, and it can sometimes help prevent eclampsia. Now, eclampsia can rear it’s ugly head for some time after she starts producing milk, and if it happens veterinary intervention and treatment is vital and considered an emergency. But in Moms that are borderline, who could go one way or the other, a little extra effort can make a difference.