More likely the amulet acts like a traditional phylactery. Binding her to life while it exists and ensuring that a death will only scatter her essence. When the ritual to revive her is performed, all that she is converges on the amulet while her form is recreated. So essentially a demon recreation ritual similar to reassembling the Fade Beast in DA:O in the Deep Roads, with Flemeth's essence --scattered or not-- taking the role of the demon. So it wouldn't matter if she lived or died in DA:O, since the ritual only calls her essence to the locket and remakes her.
If she lived, she was transposed to the amulet. If not, she was reborn.
EDIT: I know this is the wrong place to talk about that, but I hope this clarifies the issue of her rebirth.
Edited by Ocarina7, 21 October 2014 - 12:41 AM.