Caring for your pregnant Chihuahua, isn't really all that different than caring for her at any other time, as long as you remember a few things.
As for vaccinations,
do not give her any. If it is a planned breeding, either give her the boosters before breeding her, or wait until after the pups are born, but do not vaccinate her while she is pregnant, as this is not safe on the developing puppies.
If she has or develops worms while she is pregnant, you will need to wait until after the puppies are born before she can be treated.
De-wormers are not safe on unborn pups.
Any dog shots and/or de-wormings that are needed, do not have to wait until the puppies are weaned, just until they are delivered.
It is safe to give shots and wormers while she is nursing.
Many heartworm medicines, such as Heartgard, are safe to use during
gestation,
as are certain flea medications, such as Frontline Plus.
If you use a different brand, simply check with your vet to make sure they are safe to give to a pregnant dog.