I would be shocked and appalled if they tried to include her character or likeness on-screen in IX.
The real question is how to rework elegantly the overall story arc of XIII (already shot) and IX (heavily written and pre-produced) to accommodate her absence from the screen in IX.
One way would be to reference her fate in the crawl to IX, which would fit into the in media res opening sequence of the original film, but not really the rest, since none of the rest had significant story-points take place in between installments.