I mean would you be surprised about that? In Scarlet Witch #2 Storm moved some fog and Wanda then said to her that it was actual a magic barrier. She clearly can see things most other people cannot. She even states that Ororo has the same ability.
Not to mention it was a pretty big point in the Robinson run where she saw and dealt with things while most others had no idea about what is even going on.
Besides Agatha is not some stranger. Agatha herself even says she knows all about her. They have gone through a lot. Good and bad for that matter.