This is for people who find this googling bc didn’t exist for me.
Guides like maxroll show this guardian investigation quest chain for this step starts at Frost Haven. But this is incorrect or game changed since last updated guide.
Correct / actual location to start this quest is Woeful Drylands.
Yea the maxroll guide isn’t accurate for that entire quest line. Just pay attention and she will tell you where to find her after you kill each boss.
I actually Google where to find her after killing the boss. There is always some reddit post where people have already asked the same question. Maxroll is not accurate at all for this quest line, wish they could at least update it.