In this case, it really depends on what you want to do with it, in terms of story direction. RoseMultiverse is right, in the new universe, even if SBURB hasn't started yet, it still has a major and persistent influence on the universe (particularly through the first guardian, if there is one). Having a player from another SBURB session, particularly a god-tiered one who was never meant to be part of the session, could make things weird.

The implications of that, though, are up to you. Maybe Mydi was actually fated to get there all along. Maybe the first guardian of that universe is trying incessantly to kill her and she only escapes by being protected by the void, like how Equius couldn't be seen by Doc Scratch. Maybe the game outright rejects her upon entry or her land is corrupted, or maybe not. There's no definitive answer -- whatever contributes to the story you're trying to tell! ^u^