How did Kumoko know she could defeat a monster by making it run out of SP?

Question

Unbeknownst to the viewers of the anime until the reveal at the end, the crux of Kumoko's strategy against Earth Dragon Araba was to make it run out of SP. How did she know this was something she could do?

Answer 1

Note there are two types of SP: Instantaneous (yellow) and Persistent (red). The red one is the important one here. Yellow is basically just how much one can run around before getting winded, while red is metabolic energy.

I went back to the scene where Kumoko's supposed to learn this, and I have to say the anime really messed up. It isn't as though it's preposterous for Kumoko to just figure this out by guessing, but the confirmation would be important if she's going to stake her life by using it for formulating a strategy in a life or death battle. She was supposed to learn this immediately after getting her first evil eye (the Cursed Evil Eye), when testing it out on a frog. From volume 2 page 169 in chapter 7: The Administrator's Shadow:

Hmm? Huh? The frog died?

What the hell? I thought it still had some HP left...

The rest of its HP drained in a flash. But why?

Ahh, it ran out of red SP before it ran out of HP.

So that's why. Guess when you run out of red SP, your HP starts decreasing really quickly.

WHAAAT?!

Yikes. I've had some pretty close calls after evolving and stuff, then.

Good thing I had food at the time.

Thanks to Overeating, my red SP hardly ever goes down, but I'll have to be extra careful from now on

In the anime in the same scene, you can see the frog's red SP is going to run out before its HP, but it cuts away before that happens, and just shows its health. Not only that, but Kumoko doesn't really comment on the SP here at all. So, what was supposed to be foreshadowing and informing the viewer of how SP works ends up not doing either of those things.

I'd say this was a blunder on the part of the anime as far as storytelling goes. As Brandon Sanderson says, "An author's ability to solve conflict with magic is directly proportional to how well the reader understands said magic." So when the viewers don't know about the SP thing beforehand, it diminishes how impressed they are when Kumoko uses it to win.