So, it is probably more straightforward than you realize. If a drink has lemonade, no need to add simple syrups. A trick to recreating cocktails at home from menu descriptions is to remember that the first ingredient listed is the one in the highest proportion, and it decreases incrementally as the ingredients continue.
I do a lot of cocktail testing and inventing at home as a hobby. In this case, I'd hazard a guess that there are equal amounts of vodka and lemonade and then muddled berries. I'd make this drink by doing the following:
Muddle 3-4 fresh blackberries in the bottom of a glass. Add ice to the glass. Add 3oz vodka and 3oz lemonade to a shaker filled with ice. Shake vigorously and pour over smashed berries. Stir.
I'd taste and add more lemonade if it was too strong.
The most important thing is getting that exact vodka. However, any top shelf lemon vodka will do. I prefer Grey Goose Citron. Also, Disney uses Simply Lemonade at their bars, which is easy to find in stores.