As the scales aren't protruding, which is a sign of dropsy or worms, she could be pregnant. Try feeding brine shrimp or mysis as they act as laxatives in case she's constipated.

 

Looks like a gravid female. Tetras are egg scatterers and they spawn all the time. The females, when healthy, will look really fat all the time especially if well fed too.

Dropsy would be evident in your top-down pic by scales protruding. If she is that fat and no protruding scales, it's not dropsy. As for worms, it could be, but it's wayu more likely that it's just a gravid female.

 

Yea - they are def. well fed, they get mysis shrimp, brine shrimp, blood worms, spectrum pellets and flake food, I have been thinking about adding a pea or two to their diet per week... (thoughts?) A few usually get fat for about 2 days or so, but then usually deflate (I am pretty sure this is the females being egg bound and then laying), but this one has been "fat" for upwards of 2 weeks... I DID just move them from a 30g to a 75g and started feeding more, so maybe thats it... There are no protruding scales (no pineconing), fish hasn't been acting sick and there has been no change in behavior/color - guess it really is just a fat female... Thanks for the help/comments!

Em