Cherry barbs don't get pregnant; they're egg scatterers. She could be carrying some eggs. Have you seen the male trying to mate with her? If they do, they'll be dropping the eggs down on the substrate and plants. If you want to have some fry survive you should provide them some java moss to hide in. If you really want to save a lot of fry then they suggest you move the barb pair to a breeding tank and then remove them once they've dropped the eggs. They will eat their own eggs if they see them. Other fish will also eat the eggs if they see them. I have a couple of neon tetras which will follow the barbs around when they start mating. The tetras get fresh eggs.
BTW, I've got a few cherry barb fry currently also. I didn't do anything more than provide some java moss. I didn't want too many fry to survive. I didn't provide any special food. I guess they just ate the flakes.