Bettas live about 4 to 5 years average so I would say he still young sense most pet store sell them young.

Go to the pet store and get some antibiotics for fish, there are several kind for fish. Just tell them at the pet store how the fish is acting or just read the back and get the one that covers a wide range of things. 1 pill does 10 gal of water. I don't know if her Betta is in a tank or bowl, but if there is any filters in the tank, remove it before putting in the med's. The carb will neutralize the med. and you don't want that.

What kind of food is she giving him? Betta food or fish flakes? Stick with Betta food. If she over feeding him then the extra food can will settle at the bottom of the tank and will pollute the water.

Have her change to water, just in case, add what ever treatment she need for her type of water then add the med's. If she can, have her get a PH tester and make sure her PH is not to high or low.

I have to say this only because I have know so many people that when they do a water change the wash the bowl or tank with soap. Just in case she doen't know, tell her not to.

Hope I helped some.