I did a quick google search for "chihuahua whelping," and here are my findings:
CHIHUAHUA WHELPING PROBLEMS
http://www.geocities.com/Petsburgh/Park/3905/chiwhelp.html
ONE BIG PUPPY - (the singleton) This one is self-explanatory. A bitch carries only one puppy, it gets all of the nutrition in her system, and is too big to be whelped without a C-section.
TOO MANY PUPPIES - Sometimes the bitch will conceive a huge litter, run out of room to carry them. They either have the litter a week to ten days early or have a C-section because there is absolutely no room for them to move down the uterine horns or take up the position for natural birth.
MUMMIFIED PUPPY IN THE WAY - In this case a puppy dies early in the pregnancy, mummifies, and then blocks the birth canal at the time labour occurs. Sometimes it will pass and normal birth will progress but often the dead puppy is the wrong shape to pass through the pelvic rim. Often a C-section is the only option in this case.
SEPARATED PLACENTA PUPPY - This is a case where the placenta of one of the pups in a litter peels loose in the uterus. The telltale sign is dark green fluid discharge before the first puppy is born. A C-section is usually necessary if this occurs.
ANAESTHETIC OVERDOSE - Any time a Chihuahua is put under anaesthetic there is a risk that the dog's system won't cope. A long procedure under anaesthetic can cause anaesthetised puppies with depressed breathing and heart rates this can cause puppy deaths.
Because of how young your girl is, and because Chihuahuas often have problems whelping, I would definitely be taking her to the vet to see whether or not she is pregnant. If she is pregnant, I would recommend spaying
for her safety. She is far too young to have a litter, her body is not ready and she is most likely not mentally ready. Are you ready to try and hand raise an entire litter of tiny, fragile puppies if need be?
This is an EXCELLENT site I found that shows how involved (photos!) a Chihuahua whelping session is:
Birth of a Litter.
Have you ever bred a litter of Chihuahuas before?