Hi Mariah!
Has the prolapse gone away yet? If not, I would suggest that you give her a salt bath. If you have a hospital tank that you can transport her into, that would be best, but if not, then it won't harm the other fish- as long as you DON'T have any invertebrates or scaleless fish in there! A salt bath is actually beneficial for fish that can handle them because it causes the fish to produce slime which helps to heal, protect, and alleviate stress. The salt bath should help to bring back the rectum into place because it will relieve any inflammation that is keeping the prolapse outside the body.
To give a
salt bath treatment:
Days 1 - 3: add I teaspoon of salt per gallon of water, every morning and every night. (2 teaspoons /gallon/day)
Days 4 - 7: Leave water alone.
Days 8 - 10: Remove half of the tank water each day and replace with unsalted, chlorine-free water at the correct temperature.
If by day 7 you see any improvement (but not a total cure), wait until day 10 to start changing the water in the tank. Be sure to change half the water once a day, for three days at the end of the salt treatment. Also, don't wait longer than 10 days to start changing the water, as the salt itself can begin to cause problems for your fish.
There is obviously some underlying problem, which could sometimes be caused because she gave birth recently, or because of a different problem. It could be related to Hexamita, which has symptoms of white/clear poo and prolapsed rectum. You can cure it with an anti-parasitic medication, but this article makes a good point:
Hexamita and Spironucleus. It says that it could be caused by a mineral deficiency. While this might be a bit far-fetched, it's a good idea to keep this in mind, if the salt bath or any anti-parasitic medication doesn't clear it up.
I hope that it clears up quickly for your little fishies!
The reason I thought about hexamita, is because I recall that you said you had discus in the tank prior to having the guppies in there, and you did mention that they had the white poo (in another thread). Hexamita is the same protozoa as Hole in the Head disease (HITH), which occurs in larger fish, especially in oscars and in cichlids- like discus. So if the tank had any protozoa that causes HITH, it is a possibility that your guppies are affected with it as well. With smaller fish, like guppies, the same protozoa affects them a little differently, so this kind of explains the difference between hexamita and HITH. Same protozoa, different symptoms displayed.
Anyway, I don't want to scare you with that, so I'll stop right there. Sorry for going on and on!