If she is in an aquarium, you might try to very carefully net out the fry and put them in another aquarium. Better still, make sure you have plenty of places for them to hide, ideally in a bunch of live plants, either anchored or floating. As long as the fry have a place to hide, there is less of a chance they'll be eaten by the mother, which she does to deprive any predator she feels threatened may exist. They'll do well on powdered flake food, which you can do by simply rubbing just a few flakes of food between your thumb and index finger, letting the powder drop into their nursery. Better still, hatch some brine shrimp nauplii and feed these to the babies.
Guppy fry are big for fry fish and they are free swimming at birth.
They'll get stronger, bigger and faster on the newly hatch brine shrimp nauplii. In the wild, guppies eat small aquatic insects, notably mosquito larvae. This should be reflected in the food you feed them. First thing, keep an eye on them. Check with the table found at Diseases and see which condition best describes the situation and treat accordingly.