R.R.
Try shampoos with citrus in them like lemon or grapefruit, or herbs like rosemary. If a shampoo says "clarifying" it is for oily hair, Suave on up to expensive brands make them. Read the labels and look for something like "won't weigh hair down." Some shampoos are for normal to oily, they'll say on the label, she can also use shampoos for normal hair if she shampoos every day, as long as they're not heavy with moisturizers. Shampoos for "volume" are good, too, they don't weigh the hair down with lots of moisturizers. Pantene makes one called "Sheer Volume," Aussie, L'Oreal and others make them as well.
Shampoos with light conditioners built in will work better than using them separate, but if she does use a conditioner on it's own have her use it just on the ends. And, have her try a dry shampoo for when her hair looks oily but she doesn't want to wash it just yet. I got some last week by Suave (yes, Gramma STILL has oily hair!) and it works and smells great : )