Hi B.,
My daughter was born with maybe two little white bumps in her gums as well. I can't remember exactly, but I am thinking hers didn't show up right away but maybe a couple months or so later. Anyway, our Pedi called them cysts or "debris"...that they were basically tiny pieces of the bones that would eventually work themselves through the gums. They were not there for very long and I have no idea when they even came out. My daughter was never a thumb sucker but was born 8 weeks premature.
Good luck to you, your granddaughter and her mother!
-Char