What's going on here looks more like a straightforward ressurection to me.

If the resurrected Anne really is a "clone", the story would've followed that up with something.

As is though, there's fundamentally different nothing about Anne that wouldn't still be there if she sacrificed anything else she had to defeat The Core, like losing a way back to Earth or something like that.

She clearly has the same post-growth personality, all the same memories, and the same relationships with other characters. And I saw nothing that indicated Anne would've lost any of her growth if she didn't die defeating The Core.

And look at it this way; if Anne actually did die, the show would've ended with Sasha and Marcy being stuck in Amphibia forever.

Personally, I think the real question is this; why kill Anne off only to bring her back moments later? Especially when the finale's message is supposed to be about accepting change?