My miniature dachsund vomited twice now 6 hours apart. Do I withhold food ? Water ? For how long ? What should I start to give her to eat ?

It is more common for a younger dog to forage a bit of something to upset their tummy than an older dog. I would offer it its regular chow at the next meal. If it still doesn't keep it down, try:

Out of the manual I have from a large, knowledgeable dog guide school.

Bland recovery diet for dogs.

3 parts cooked rice, one part boiled hamburger or chicken, or cottage cheese. I think you can substitute boiled potatoes for the rice. Once in an emergency, we bought a plain baked potato from Wendy's.

This is meant for short time settling a dog's digestive tract. It is not the complete and balanced they need long term, nor meant to tempt a dog to begin eating before it is ready.

Unless the dog's ribs are already showing, a day or 2 without eating won't hurt it. The worst thing you can do is tempt a dog to eat by offering it rich food.

You have a day or 2 to see if this clears up. If not, call the vet. If it is showing sign of pain or otherwise disturbed, call the vet now. Don't put off too long, you don't want to go into the weekend with a sick dog.

From the housebreaking sticky: A couple big putty knives
Work well on bowel movements. Just slide one under it while holding it with
The other. This gets it up with a minimum of pushing it down into the carpet.
This works with even relatively soft ones, vomit, dirt from over turned house
Plants, or anything else from solids to thick liquids. Finish up with a good
Shot of carpet foam. Note, do not let the puppy lick up the carpet foam.