I've tried looking up some information now and from what i've read dropsy or symptons of it show with a number of things that can be wrong with your fish, some sites even said it isnt actually a disease on its own just signs that something is wrong with your fish be it physically, bacterially or enviromentally. are its eyes normal? they also said dropsy usually they have popping out eyes.
You can check your water quality and make sure the stats arent to high for the fish ie ammonia nitrites and nitrates, you could be lucky and it just be a warning that something isn't right with them or that it is the constipation cant harm them feeding them peas for a few days then move onto bloodworm just stay away from flake and dried foods, or an internal bacterial disease, in which case treat the whole tank with meds( i dont know anything about these). some sites say there are meds that you can buy but others say there aren't
but then you need to find out what is causing it before you can treat it properly and with anything its simple to rule out the easiest ones to test first. then again she could be eggbound. Is there anyway you could take either a pic of her or her to a LFS or call them and ask them about it?
I've been looking at my female danio and shes fat and due to spawn at some point but no scales are pineconing. I need another tank set up with marbles before Im gonna get to save any though.
I asked at my lfs about the dropsy when my tetra showed signs and he actually said that if it was dropsy more then one fish would show symptons of it and that it had probably been pigging out on fry etc in the tank and suggested the no dried foods diet for a week.
Does the fish still swim normally and still act active? if it is Id leave it where it is as it would get more stressed being in a confined space then out acting normally. or if you have one move it to another tank (if you want to be extra safe but then if it is ill with something that needs meds you'd need to treat both tanks.) so it would be worth talking to a LFS that know about fish disease etc
If its being harassed and picked on then move it to a breeding trap or cycled quarantine tank.
hopefully it is just constipation and your fish gets better soon