All food is 'good for you' in tha.t it contains carbohydrates, proteins, fats and mineral salts in varying proportion. Roughage is also very useful.
Cooking can remove or alter some of these properties but has the added benefit of making the food more digestible.
Your jam will be incredibly good for you - in small amounts as it's full of sugar.
Even refined sugar is 'good for you', especially if you're starving or having a hypo. It's just that it's also addictive, so you start to crave more, and that isn't good for you.
The elderberry part of your jam may have retained some of its laxative qualities, ensuring a healthy transit through the gut of today's intake, so again, good for you in moderation.