Now I badly want a "timeshift" episode. Set in Beach City a century or two in the past, it would feature the Crystal Gems interacting with the ancestors of the characters we know, who often look and sound the same as their modern counterparts. So there would be another Dewey being the mayor, Sadie's and Lars' ancestors/lookalikes running a bar, Greg's ancestor running a… whatever would be an old-timey equivalent of a car wash (even though Greg was a travelling musician passing by, his uncle and aunt had a barn just outside of Beach City, so his family too might have roots in Beach City), etc.

I know this kind of sounds cheesy, but I think it worked incredibly well in Phineas and Ferb. Besides, Captain William Dewey seems to have looked almost exactly the same as modern Mayor Dewey, so this wouldn't be that much of a stretch.

I'd say it'd only really be weird if she knew him back when he was 3… or 0…

Maybe if she also "knew" an ancestor of his too… But that's a bit of a grey area.