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Absolutely, positively it is not pregnant. As Tetras are egg layers, they can never be pregnant. They can carry eggs ( which may be what you fish is doing), but if there are no males in the tank and the proper conditions for spawning are not present in the tank, nothing will come of her holding eggs.
Hope this makes you feel better
If this is not a balloon variation, the fullness in the abdomen would mean it's a female. Males tend to be slender except right after eating. Females will be rounded all the time.
It's not necessary unless you plan on breeding them. It's nothing like doing livebearers and takes effort on your part to have a successful spawning and raising the fry. Egglaying fish can hold eggs their entire lives and never spawn so that fact that she is carrying eggs is not really a concern.