The female guppy is not normal, not even for a pregnant one that is about to give birth. She could have worms in addition to being pregnant, or maybe her swim bladder is being distended by the babies in her, but she should not look like that.
Do not add medication unless you know what the problem is, it can also cause problems especially to pregnant fish. And she is eating and swimming about so that is a good sign.
If you have a small tank put her in it and keep her away from the others. Use a net to bring her to the surface then use a small container to scoop her out. If you lift her out of water she could have problems especially if she is close to giving birth.
Have some floating plants in the tank and monitor her.
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re: feeding. You should feed more variety, add the frozen bloodworms and brineshrimp every couple of days or even every day. Feed flake first, then 15 minutes later give them some brineshrimp. The next day flake then bloodworms. If you get some frozen raw prawn, you can defrost one, remove the shell and use a pr of scissors to cut it up into little bits and offer a few bits at a time. Do this a couple of times a week.
If you find aphids on the flowers in the garden, tap them into a bucket and feed them to the fish. Mosquito larvae and adult mozzies as long as they are free of bug spray, are also good food.
All suckermouth catfish need driftwood in their tank. They eat it and the roughage heaps feed the beneficial bacteria in their gut and helps keep them healthy. If you have suckermouth catfish (bristlenose, plecostomus, whiptail, twigs, algae eaters of any sort), make sure you have a piece of driftwood in the tank.
They should also get plant matter each day or every couple of days, depending on how much algae is in the tank. No algae then feed plant matter every day. Lots of algae then feed plant matter every few days. Good food to try include thin slices or cubes of pumpkin, zucchini & cucumber, apple is sometimes eaten too. Wash well and if possible peel them. Just make sure they are free of chemicals. Put the piece of food in the tank and remove it after an hour or so. You can leave it in the tank over night if you like but most fish will respond to it within minutes of going into the tank.