Have her do 100% water changes at least once a day, if not twice maybe three times. Each goldfish would need about 20 gallons, so obviously as many water changes as possible will help. I'm not sure, but I think petco might still have a dollar per gallon sale going on. that means you could buy a 20 gallon for all four (until they grow some more) for less than what a 10 gallon kit would be. If you know any people who have any decent sized backyard contained ponds that they keep good care of, you might even want to consider rehoming those goldfish.
I've grown up with goldfish in my backyard pond, and six or so years ago they were 1/2 an inch feeder fish. Now, they are easily 7 to 8 inches long.