Felltree Marsh I'm left looking at the glowing ends

They were south of here, yes? If she was right, the pack resided in the forests just south.  She'd never visited, but had passed, as the area was close enough to Ankyra to be of interest.  You say they left, but perhaps they left a sign.  It was a goal, and this was what her mind latched onto.  It hadn't occurred to her before to assess the surrounding packs, for Rusalka hadn't had any allies.  But if Erzulie did survive, she'd have taken the family inland.  She'd need a pack, and wherever they were, Rosalyn would join them.  Even if it meant passing the winter alone.

It cannot hurt to search. Could not hurt her at least.  She didn't know his thoughts or reluctance in returning.