i still need a visual set up to understand this.

HA! i was just thinking the other day, " why hasnt mongomcmichael uploaded the door scene?"

Her logic is faulty.
The problem of course is, that you don't know if the one who explained the riddle to you is the one who tells the truth or the one who tells lies.
So, there are actually two possibilities:
One tells the truth and one lies or both lie. (It isn't possible that both tell the truth because in that case it would have been the answer).
So, if one of them explains this setup to you, you can only be sure of one thing: The other one lies. The way to solve this riddle is therefore to ask the other one and do the opposite of what he said to do.

Surely she gets the riddle right though, because the way she goes does NOT lead to certain death?

Can't you just ask them if the sky is blue or something?

They cut this off too soon.