This is both the trickiest and most diverse of her weapons. I've already figured on three play-styles with it.
1. Just shoot it like bullets and hope for the best because this weapons is very spammy and can simply be used as a bullet hose with massive bullets. This is very inefficient and doesn't reward the player with good damage but you'll still net some damage and mixed with a melee card that triggers after a shot can still set you up for good damage.
2. This was best pointed out by Milky in that you want to do a two shot combo by shooting once with a lower or precise bounce then detonate it with a second tap on sphere for the AOE blast. This is by far the most efficient damage wise but it's also the trickiest and even after explaining this mechanic to individuals they do seem to struggle with it quite a bit.
3. Last but not least, you simply work on your bounces to get as many as possible per shot or mag and likely get random AOE in the mix. While neither worst or best, this is how a lot of people 'seem' to be using the weapon as the bouncing/growing mechanic is very easy visually to grasp.
Why use just one style? Different situations might warrant different styles over another either because you simply don't have time or the set up required. If you're going to actually practice this weapon, less spamming and careful explosions or multiple bounces will get you further. Ergo, try not to dump your mag but also keep in mind this gun is full auto and will do that with little effort from the player.