I wouldn't be too sure of that. She might have started off as a copy. But a copy still has all (some argument on this) of her memories, and a fallen would only be as strong of the vessel they're wearing.
And, since Lash had been using Harry's lifeforce/energies to sustain herself AND Harry now has access to soulfire (using his soul to turbocharge spells, turning it from passive existence to active usability making many of his spells more real) perhaps Lash can also use it to rebulid/heal or make herself more than she had been. Also, Harry has a tendency to take on those with considerably greater power and eek out a win or at least a non-loss.
Should that house of cards stand, the question then begs to be asked.....Did Uriel know Lash was still around and that she would be able to use said soulfire to help herself and that perhaps her self sacrifice was worthy of a little help....and add another layer of future toughness that Harry will need by the time the BAT rolls around.......
Or maybe I should have just gotten more sleep last night......