User blog comment:Legendary Pop-Fizz/What new properties do you want to see in Earth 199999?/@comment-1659166-20150716032948/@comment-4651179-20150716033539

She's a mutant, but not an X-Men character.

If Marvel could use Scarlet Witch and Quicksilver, who had a strong link with the X-Men, I doubt they couldn't use Squirrel Girl, who even originated in an Iron Man comic.