There is no way CB Cebulski forgot about her. He had her as a main character in his Loners mini-series and wanted to use her again. Nick Lowe brought her up in an interview regarding Spiderverse. Mattie had a small cameo in Spider-verse, appeared on the front of the Spider-Gwen #1 variation cover, and recently they reprinted Alias in response to the Jessica Jones show hype. So they do remember her, its just that at the time Quesada didn't want to remind readers too much that there was another Spider-Girl that had a brother-sister relationship with Peter and who was mentored by Jessica Drew that wasn't Anya.
And yes, Grim Hunt was Quesada's idea according to Joe Kelly in an IGN interview and it shows by the creation of other Spider-Women after his leave as editor-in-Chief. Which is pretty sexist when you think about it. Considering how many Spider-Men were around at the time(Peter, Flash, Kaine, and Ricochet). With Quesada no longer as EIO there is a possibility of Mattie showing up since she died in the same story where Madame Web was killed.