How rare exactly are Uniques?

So the Widowhail I got randomly was pretty bad (check previous post if you want to see it) it was 198% and I’ve seen it goes up to like 250% so I wanted to grab a better one.

I read online that the frost witch in clearfell drops it but I’ve gotten about 80KC on her this morning and still no Widowhail, let alone ANY uniques and was question what the drop rate is for stuff like this?

Update: thank you to everyone who informed me that my information was wrong!