It will still do no damage, Except if the Firesword user has Guard and Flashing/Heavy Blade. Guard so she can´t use Aether as fast and Flashing/Heavy Blade to circumvent Special Fighter.
You dream emptily. Firesweepers usually have at least 53 atk, which counts for 63 against her. That's only 5HP short of a one-round. And I said at least 53. I've seen higher than 60, in which case two wards might not save her.
Well, I mean, unmerged uninherited default neutral atk selena kills her in two rounds no matter what the attack pattern is, so no, not even close to invincible.