Let's not understate the importance of familiarity of the dive site. Familiarity leads to comfort. It also leads to complacency of course...
I can only speak of my personal experience, but because I tend to dive in Tobermory a lot (I have had a place there for 32 years) I am guilty of diving the same sites a lot. I suspect I have 350+ dives on the Arabia alone. A popular deeper wall dive is at the site of the Lady Dufferin. There is wreckage in the shallows (30' - 90') followed by a vertical wall that drops from about 90' down to 180'. From there, there's a steeply sloping bottom down to very great depths, with more wreckage.
I would say I dive that site 15 - 18 times each season. Almost always, I bottom out at 175' to 180'. I am on air, but wearing doubles with some sort of deco gas slung in a 40. I don't normally feel any narcosis whatsoever. Normally... but not always. The odd time I do feel narc'd, I would call it a dark narc. I feel uneasy, so I bugger off upward and within 15' to 20', I'm right as rain.
Typically, my bottom time is about 15 - 18 minutes, followed by a leisurely trip home, for a total run time of around an hour. I always have more than half of my gas supply left.
Anyway, my point is that I feel 100% comfortable on that dive, 99% of the time. Others who are perhaps diving there for their first of second time might feel otherwise. It's usually very cold, fairly dark and sometimes there are strong currents.
I imagine that this woman feels about the same way regarding her dive.
Here are a couple of images from the Dufferin Wall. The distant shot is at about 160' and shows most of the vertical wall. The second is at about 170'... basically the bottom of the wall. From here, it's a sloping bottom down to well over 400'. And yes, people have died here.