You can now invite Shauna as a Guest to the Trainer Lodge in Pokémon Masters EX by first teaming up with Shauna & Chesnaught, Shauna & Delcatty now available as a new sync pair

DeNA is continuing to add more events and new features to Pokémon Masters EX on a regular basis. Read on below to learn more:

A New Guest Arrives in the Trainer Lodge

Starting October 31, 2024, you’ll be able to invite Shauna as a Guest to the Trainer Lodge! To invite Shauna, you’ll need to team up with Shauna & Chesnaught first.
You can team up with Shauna & Chesnaught via various Sync Pair Scouts, so be sure to invite her once you’ve teamed up with this Sync Pair.

Source: Official Pokémon Masters EX site