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I believe that the city that Enclave grew up in (Guallidurth) would prioritize torture over direct murder as a means of social control; The city at the time that she was apart of it was 80k to Menzo's 20k. In combination with the ruling houses having less immediate control on the way Lolth is worshiped, I think there's a stronger prioritization on not killing the people that one has folded into their house. It's just a matter of having bodies - Unlike Menzo, which uses death as a means of social control, if you're killing the people you have in your house in a place that has 80k people, eventually the house with more people is going to catch up to you.

So focusing on punishments that force people in-line is more adventitious (but leaves open the possibility that they could escape, which is showcased in the way that the city has more explicit sects devoted to other gods that they can't seem to cull.)

IE, Enclave didn't get killed after she was discovered to be a traitor only because the social conditions that she grew up in allowed for it; If she was in a place like Menzo, she would be dead.

As for the tattoos themselves.

Enclaves tattoo's are punitive in nature (based off a mention by Ed Greenwood that most drow have an association to tattoos as something given to prisoners and slaves.) Each part of her tattoo means something different, with the larger design on her forehead being indicative of being discovered as a traitor, and the smaller notches being a more general punitive marker. The external ones are the sign of "punishment" and the internal ones are a sign that she was a ranking priestess, and is now no longer to be granted for the title.

I think this one is regional to Guallidurth; A drow not from the city would be able to tell that they are punitive in nature, but not specifically what they were given for.

The fact that Enclave hasnt removed them is probably seen as odd to most people. There are magic ways of doing so, but (the two fold reason for her not doing so) is that it both never organically naturally occurs to her to change her appearance again, and that at a glance, most drow can tell that she is not on Lolths side.

And on an authorial side of things, that is a purposeful deconstruction of WizCo continuing to try and push ways to tell apart drow who are Killable and drow who are Not. A drow would be able to tell that distinction, but to any outsiders, the spider markings just looks like more devotion to Lolth.