I may be new to this sport, however I do educate myself about the animals that I have. IMO I do not believe she is gravid, if that is a Pachytriton labiatus (Chinese Paddle Tail Newt) it appears to be too small to reproduce from all the information I have gathered. I have one of my own who is well over 6" long and as of present, people on this site have not been able to guess the sex of it because they feel it is still too young to sex properly. Your tank seems to have no filtration, too little water, and since they prefer moving water, the condition in your tank currently doesn't provide for a healthy environment for your newts.
Are you sure it is a female? If it is, do you know how old she is? How long have you had them? How much and how fast is the filtration in your tank if any? How often do you feed them? What temperature is your water? What are your water parameters?
P. labiatus are completely aquatic, they absorb oxygen through their skin, as well as through their lungs by gulping air from the surface of the water. They should be kept in water that is between 15 to 18C (60 to 66F) respectfully and the cooler the water the better. Feeding too often can cause obesity in your animal, feeding once ever three days is acceptable and it all depends on how much you feed them at a time. They will over eat if you allow them to. You said you had two of them, is it possible that they are both males? The smaller male may be being bullied by the larger one and since they are very aggressive eaters, this could be why one is fatter then the other. They will compete for food in the tank and one will inevitably loose out when battling for food.
Here are a few people you should get in contact with are Greatwtehunter, Michael, BC, Otterwoman, and Abraham. They are very knowledgeable on them since have a few of their own.
