I definitely wouldn't use a martingale on a Chihuahua. It still chokes the dog a little, even though it's not as bad as a regular choke collar. A regular collar can hurt a Chihuahua's trachea, never mind a martingale. Some people call them "humane choke collars." They definitely have their place, but not with small dogs like a Chi.
What may help with her instead of a pull correction is just reversing your direction, so that she is not rewarded by getting to where she wants (instead she goes the opposite way). It also helps teach her to pay more attention to you.
You can also try telling her to sit when she gets close to the end of the leash. When using pull or sit as a correction, it's very important to do it before she gets to the end.
If you take her to a basic obedience class, they will teach you the proper way to teach her how to stop pulling on the leash, as well as many other beneficial things, and you'll be able to get her to pay more attention to you.
These are excellent to stop your dog from pulling. They work great with our 60 pound pit mix: