Here is the schedule for Texas:
General Pet Care Tips - Vaccinations - SPCA of Texas
She is 4 weeks and you have her at home? Or is she still at the breeders?
If you have her she is too young for vaccines, please be aware you should not take her anywhere.. If you have an un-fenced yard and you know dogs roam the area I would take off your shoes when you go into your home. Parvo virus can get on the bottom of your shoe and you can take that into your home.
When you want to get her spayed is pretty much up to you. Usually people will get them spayed between 5-6 months. With females they say you should spay them before their first heat cycle, which varies for each dog.
The weight isn't really a factor. Some people do wait until they weigh 4-5 pounds, some don't. It is a personal choice, however I would go with a more experienced Vet. One who has done spay surgeries on smaller dogs.. Research the Vet, get the pre op blood work and exam before getting her surgery too. The Vet should go over everything with you..