Well, we've got a Gryphon who is revered like unto a god in this setting. And he gave Almus his blessings, which were a real thing. So a jorougumo type girl doesn't feel like too much of a stretch at this point.
the whole blessings system feels very lazy, kinda like the author changed their mind and didnt like them halfway through.
Blessings were a core part of the early ch but then kinda completely fell out of relevancy and are never brought up after the whole backlash thing when he got crowned as king.
Sure its the main reason why mc is able to fight, but it was also stated that the blessing of kings strengthens the holder based off how many people follow him, however we havent actually seen much change nor is it mentioned even after all this time where his follower number has exploded (think about it, he was able to crush trees with his hands with only 100 people following him from the village, now he has tens of thousands).
early on they also made a point that entities could have multiple blessings and yet it seems exeedingly rare for people to actually have blessings so why bring up that point, and the blessings people do have seem to be devices that are convienent to the plot rather then individual characteristics.
all in all i would say the spider chick is very strange outlier as no mention of demihumans has ever been made till now in addition to what i think above on blessings (also the fact that from what we have seen of blessings, they werent things that let you manifest physical objects like webs.) id wager she is just a plot device as the story falls into the typical escalation trope (every threat/issue has to be bigger or more dangerous then the last) that is so very common in stories.
