Rich Morris' Comics - YAFGC and The ComixBlog

And yet three of the others got past without getting killed. Arachne surrendered mobility, agility and the fact she was already in motion to pretty much order some orcs about, in the middle of a war where the orcs are trying to obliterate the drow and the drow the orcs.

I reiterate: Stupid Evil.

Nephilia spent the last, what, fifty years in the Abyss, and she knew to run for it. Anancy had spent less than an hour under the mountain, and she knew to run for it. Wolf, a dedicated survivor, ran for it. The only other one to hang around was the kid, and I suspect she only didn't run because Arachne didn't.

I don't think they ran past Glon and his wives, because otherwise they would be killed outright like any other drow. Maybe they somehow missed Glon (perhaps there are two passageways behind that exit?) and thus escaped. But when Arachne approached to the exit, it was already blocked.
Therefore, she had no way to dodge the orcs. And even if (with extremely good luck and some acrobatic tricks) she had somehow managed to slip past, she couldn't be sure that Sittica would be able to repeat this feat.

If it was anyone else than Glon attacking her maybe she would flee but less than an hour ago they were allies in a common mission. Neph, Wolf etc saw an agry orc but Arachne saw an angry friend who had no reason to be there for her.
Sure, a smidgen of her pride could be a factor, but i do not think she acted stupidly on that one.

We know the others were blocked by the G&G crew. Rich drew it that way.

Also, the blood-spattered armor should've been a big clue.

Really, more people should study Jack Sparrow. Anyone know which quote I'm thinking of?

Actually, he drew it so that it looked like the others escaped right before the orcs arrived to block it (in the strip Odisseus linked to). The time delay between them running and Arachne and Sittica turning to run is key.

As for blood-spattered armor, it would be irrelevant. The mountain is in the middle of the war. Arachne would have no reason to assume other than that they ran into some resistance on their way to the cavern she was in.

If it were an issue of survival and if Arachne had been committed to running away, I doubt she would have given a moment's thought to Sittica.

In rare occasions Arachne can be altruistic.

Sure. But the occasions are rare and not easily predictable.