Oh no...! I think he'll be brought in from Earth-19 the same way she is. There's only so many times she can tell the Earth-1 heroes about her cousin before they actually meet him, right?
And I think they'll do the same with Batman. The Bruce on Earth-1 might never have become Batman, while batman on Supergirl's earth has been teased many times.

And thanks for reading! Was so surprised to see this comment 😃