Generally, you shouldn’t. Her Burst’s Ice Shards consume Pyro auras, preventing Ganyu from triggering Melt on both hits of her Charged Attack. However, there are some scenarios where this isn’t the case: When Jean is applying Pyro via Sunfire. When there are multiple Pyro applicators (e.g., Xiangling’s Pyro application combined with Kazuha’s Pyro application.). When enemies are far enough from each other to avoid taking multiple hits from different Ice Shards. Note that Xiangling’s damage at higher investment levels can compensate for Ganyu’s missed Melts, since Xiangling can Melt leftover Cryo auras. However, this still results in lower overall damage compared to not using Ganyu’s Burst.