We always did pre-baby vaccines at about 6-8 weeks out but if it's off by a little, you are still OK. It's harder to calculate when you don't know exactly when they were bred and/or they go over the due dates...
She is looking awesome, I'm excited for you.
I, too, am getting close to having two new ones. The 3rd mare is much smaller now - so part of her "belly" wasn't the foal itself but was due to being way heavy (fat). the running from the other ponies has trimmed her down nicely and I think we are looking at a mid-May/early June baby with her which matches the July month that the Mom noticed she was being mounted in the pasture by the stallion.