My dog had 3 puppies yesterday morning is it possible for her to still have more inside her?

Why do you think she might? Litter sizes can vary a lot.
Small dogs tend to give birth in a few hours and big dogs as much as 8 hours, with a few taking well over 24 hours.
A dead puppy left inside can result in peritonitis, and kill the mother. Placenta and/or a sac left inside can cause serious problems too.
So you tell us what her symptoms are?