It may be stuck a little. Have a taste, and give it a while - there's bound to be at least some gas being produced by it, though the first week is usually vastly busier than any subsequent time. Take hydrometer readings (corrected for temperature) daily and if it's the same three days on the trot, it's stopped for some reason. It may have finished, or it may have ended prematurely. You'd be looking for an FG of around 0990-0996.
If you'd like to restart it, something like Gervin Champagne Yeast (GV3) would be perfect. You could mix up a starter in a big bucket; dissolve some sugar (not sure how much - maybe enough to bring your SG to around 1020), and yeast nutrient (20 teaspoons) in warmed dechlorinated water, and when it's cooled to 20-25°C, add the champagne yeast, then cover. After a few hours you should be bubbling away like there's no tomorrow; give it a final stir and mix in with your elderflower. As you could need a fair bit of sugar, you might like to add most of the sugar to the stuck wine, and only use a kilo or two in the starter.
That's my opinion anyway :) Hope this helps!
