Is this after feeding?
I would say it was acting like a little pig and ate too much. I have a couple of rummy's and neons that do that! They are quite the hungry hungry hippos!
No it's been like this for a week or so getting slowly bigger and my male rummy noses keep chasing her??
She could be filling with eggs but tetras are egglayers rather than livebearers so they don't get pregnant.
Ok thanks BottomDweller
Tetras lay eggs, so no, she can't get pregnant. She is, however producing eggs, and the male is after her because he wants to fertilize them. If you don't want them to breed, then just them alone. They'll eat the eggs.