The first thing I would try is Espom Salt, which relieves bloat and constipation.
Tell your friend to get Epsom Salt, and let him or her know that it can't be Aquarium Salt, because it's not the same. Epsom Salt can be found at any drugstore/Wal-Mart etc.
Use one tablespoon per ten gallons, and treat half of the tank's volume the first day, and half the next day. Within three to five days from the second treatment, you should see results. If you don't, you can move on to more serious treatment. You can also use a stronger concentration of the Epsom Salt if you would like -- anywhere to three tablespoons per ten gallons would be fine.
If the fish is eating, try to get it to eat peas. This will also help.
Make sure that Ammonia and Nitrite levels are zero, and that Nitrates are below 20.