We have a 13 week old Westie pup (female). How much total food should she be eating each day (in tablespoons/cups/ounces)?

Even if I had 13 week old female Westie, what mine needed might not be the same as yours needed. You should be feeding a puppy chow now. Likely a half cup for each of 3 feedings a day. Switching to an adult chow for the larger breeds at 4- 6 months, slows growth and helps develop sturdier
Joints.

Puppies all too frequently come from the breeder too fat. Even young puppies definitely should be narrower at the waist than the hips and chest.
You should be able to easily feel the ribs, but not see them. Each dog is
Different. Standard recommendations are a good place to start, but each dog
Must have its food adjusted to its individual needs. See
http://www.purina.com/dogs/nutrition.asp?article=292.

The dry dog foods are actually better for the dogs. It helps keep the teeth
Clean, and exercises the jaws and teeth. If you feed a complete dog chow, you
Shouldn't need to give the dog anything else. Various people foods may only
Add more calories without providing proper nourishment. Look at how many of
Us are too fat too. If you don't want to pay name brand prices look for
Certification of passing the AAFCO tests. Make any changes in diet slowly
Over about a week.

The premium, concentrated foods give you the assurance of a brand name. They
Produce a smaller, firmer stool that is easier to clean up. It is easier to
Maintain weight on a finicky eater. The lower cost foods may actually have
Lower fat and be better for your dog. Many dogs would enjoy eating the larger
Portions you have to feed .