Any healthy dessert alternative, depening on what you like. She can make something homemade that uses healthy ingredients, like skim milk and splenda. Something like fat-free chocolate pudding is low in calories. You can find many dessert recipes online that are low in sugar/fat/calories. Chocolate covered fruit is also great, use dark chocolate, fat/sugar free jello with real fruit, cookies made without butter etc...
You can turn any dessert into a healthier version.