2
AFAIK:
If you let her burn the Erdtree before accepting the Frenzied Flame (FF), she never appears again for obvious reasons.
If you accept the FF before burning the Erdtree, do not quell it, and get its ending, she will appear in short cutscene, promising to kill you.
If you accept the FF before burning the Erdtree, quell it, and get any other ending, she never appears again after leaving you, so there is literally no way to know what she is up to in this case.