I see her weakness being the element of surprise.
When she's not in her "glowing" form (not sure what you call it), she's just a regular human, and if somebody catches her off guard for a split second, a knife to the heart could be a possibility.
So that's her kryptonite, that she's a regular human when not on guard.
Eric Bana has the same weakness when not in Hulk form. Both could be killed in their sleep if caught truly off guard. Where as heroes like CA and Superman would be fine in their sleep because of their super strength, and other heroes like Ironman and Antman could just sleep in their suits, and Scarlet Witch would be able to sense any danger even when sleeping.
No, no, and No.
1) Carol is never a "regular human." The glowing is simply a visual cue; it does Not mean she's "powered up." No idea why you thought that.
2) The Hulk (movie or comic) cannot be killed as Banner that easily either. There are many proofs of this, I'll point you to one on-camera example: He describes how he was "at a low point," and tried to commit suicide by firing a bullet into his mouth. In his words, "the other guy spat it out."
3) Wanda doesn't have a sleeping spidey sense. Not in the movies or comics. Again: no idea where you got that idea.