What is Scarlet Witch’s weakness?

It's a glass cannon. Some sneak attack and she's gone. She is physically 100% human so she can easily be taken out if she can't see it coming: invisible gas attack, long range sniper, laser through the head, safe dropped from height. Unlimited list.

If she sees an attack she can probably deny it, but if you went up to her and the sucker punched her as a human level attacker as well you could take her out.