When she destroyed the theater, they ended up outside of the universe that the theater was in. If it had merely destroyed only the theater, it would have just left them stranded inside of the dimension. "Theater of Domination" is just the term used for the entire dimension by people. You can see...
There's a surprising amount if universe level and above feats and statements in the series.
- Kevin creating a bubble universe
- The Core of Reason destroying multiple bubble universes
- The Herrscher of Domination creating a universe
- The Star of Eden destroying the Herrscher of Domination's...
Mei is the Herrscher of Thunder, which means that she has the power to control electricity.
She scales above characters such as Siegfried powered-up on Activators and a Honkai core, who was able to do this:
She's stronger than Avrora, who can create hurricanes:
Much weaker characters...