But she was halfway around the world at that point, seems like an unlikely choice. (Also Illyana has mental shields that not even top telepaths can get through without her permission.) This does remind me of the time when Jean transferred her mind to Emma's body to escape death, so there is precedent for the concept.
It's the permission angle that allows for the idea of being her being a traitor because she knew and didn't tell. Being halfway around the world shouldn't be an issue for a teleporter, especially now that it seems that now all someone has to do is say her name and they are whisked away with Illyana nowhere in sight. I agree with it being an unlikely scenario since there no reason Xavier would reach out to Illyana. Unless her incomplete soul leaves more storage space.