Witches are just humans (and other creatures) that learned to do magic. Remember, the Ancient One said that anyone can do magic.
What Wanda is first & foremost a mutant (although they haven't said that yet), with her mutant power kicking in once that Stark missile was seconds from blowing up. Most mutants powers activate that same way.
The second thing is that she is basically an idiot savant manipulator of chaos magic. To the point that she doesn't need items or spells to focus the magic, it just naturally comes to her. Notice Agatha needed sigils, wands, strands of hair, etc. to work her magic. Wanda just loses her temper...LOL.
The whole point of Agatha putting her through all of this is because she couldn't believe how powerful Wanda was without any "witch" history.
Another thing I think everyone really missed is that Wanda might have reconstituted the Mind Stone. Earlier, she stated that she couldn't "feel" Vision when she was around his body. Previous movies showed that they (Wanda & Vision) had a bond where they felt each other all the time, like soulmates, due to the Mind Stone. When she went to Westview & released all that grief, she basically pushed the mind stone (which was reduced to atoms) back together (by warping time/space (notice how the tornado around her when she built the house is just like the Aether & Thanos' teleportation portals, just red) & formed Vision's body from it.
It would explain why she can't control Vision at all. Because the real Mind Stone is in his head.
Episode 9 is gonna be amazing.