a creature is unlikely to be able to produce enough power to make a functioning weapon, considering we can barely make a laser weapon ourselves. It could also never evolve naturally as no doubt it'd require a lot of specialized evolution that wouldn't benefit the creature for a long time.
Considering the backstory of this creature, and it's "species" in general, as a type of self-modifying hive mind, the idea of "natural" is not really applicable here, so that's one constraint lifted. And these lasers are, relative to the creature itself, very, very small. They're going to be contained in the spider's hairs, so it will only end up using a very small amount of energy compared to the creature's total energy output.
You can use organic semiconductors and organic dyes as the gain medium.
Sounds like the best and most reasonable option. A ring of electrocytes generates a current, while some other cells produce large amounts of a highly conductive protein or use proteins to create large amounts of the appropriate compound, which end up filling the area between the electrocytes. Meanwhile, yet another group of cells, separated from electrified area by a filter that removes most wavelengths from the light passing through it to the gain medium, produce a substance akin to luciferase. The only parts I can't figure out is how to a: make the mirroring around the gain medium and b: how to stop the gain medium's fluids from falling out of the laser.