Glofish swollen belly?

[bluefishfriend]

Hi friends - I have a freshwater tank that’s been pretty stable for a while. We have four glofish and four tetras. A few weeks ago the blue glofish got a swollen belly (see pics). She was still peppy and energetic so I though maybe she had eggs? But it’s been this way for a few weeks at least now. Seems to be mostly on one side. I’m a mom of two and honestly don’t know much about fish. I change the water 1-2 times a month and test it and it looks okay, and the other fish are fine. Is she sick? I’ve read about dropsy and a couple other possibilities and don’t want to medicate the tank unless I really need to. Thanks for any advice you may have!