Why?
Black Heron couldn't know that Webby is the genetic creation they made years ago. She aged and never left the mansion for a long time.
And also Black Heron had not body contact with webby in episode 14 of season 3. She fought whit Srooge while Webby was with Dewey the whole time. So she took the feather from Scrooge and found out that the clones looked very familiar. And that's why she wrote "near perfect clones" too.
What do you think about it?