So according to Tv Tropes Kitty Pryde as Shroud was supposed to be in Ultimate Spider-Man's main cast instead of White Tiger and Luke Cage according to this poster released in 2011. She's at the bottom right in between Iron Fist and Nova.
Most likely it was legal issues with Fox at the time that kept her from being used.
It's funny that after the release of Into the Spider-Verse that the marketing for the 2017 Spider-Man cartoon is trying to match it... by forgetting Anya is also part of the 2017 series.
A trailer for Spider-Man related animation from Marvel HQ on the Far From Home Home release excluded Anya from clips of Marvel's Spider-Man and Marvel Superhero Adventures. Only focusing on Peter, Miles, and Gwen.