Is it possible she is reverse sneezing? There are videos on YouTube so you can see what it looks and sounds like. If that is what it is, you can try putting the palm of your hand over her nostrils for a couple seconds to help interrupt the cycle. Also, make sure you use a harness rather than a collar if you walk her.
Otherwise, I second what Susan said.
First time Chihuahua owner with many years of dog experience!