“She is quite rounded and keeps sitting in the plants, she is housed with a male but i haven’t seen any activity between the two of them. The male newt eats more than she does, so I’m not sure if she is fat.”
If she has stopped eating she could have a blockage or stomach problems. This can be caused by a parasite or even old age (many common reptiles/amphibian pets die due to stomach issues, with very bloated, heavy stomaches).
Often reptiles and amphibians will become bloated around their stomach area due to intestinal issues like a blockage from something they have eaten. With a newt there is no real way to fix this that I know of but I’m no newt expert, per se.
She may be pregnant. Or egg-bound.
But if she is lethargic, eating less, and swollen looking it’s probably impaction. (See number 12 on this FAQ site for some basic info). “Captive amphibians can accidentally swallow some of the substrate they are being kept on while they feed. Certain substrates, such as gravel or small pieces of bark, can become lodged inside of the stomach or intestine and cause problems. Amphibians that are fed a diet that is very high in chitin can also become bloated due to impaction. Sometimes whatever is stuck inside of the digestive tract will work its way out on its own, but more often this health problem requires surgery to fix.”