The files she passed me have not been copyrighted.
attaches to a work the moment it is fixed in a tangible medium (i.e. written down, put on CD, sang, etc.). However, copyright only attaches to the “stuff” that is eligible for copyright which is perhaps the entire work or just a small piece of a work.
However, before one can sue for copyright infringement
, one must how a valid Registered copyright.
Thus, registering a copyright is required to file suit to protect such copyrighted work.
Do I have any rights at all to continue to use the new files I have created while with her. She has stated that anything I uploaded while we were together is mine. That it is my "artisitic work". If the finished textures are my artistic work that who property are the files that I created using layers from both of us?
The actual answer is very fact specific. That said, I believe you can still continue to use the “new files” as those works either belong to you or to both of you (joint work).
That said, anyone can sue another for any reason (no reason, good reason, or bad reason). Thus, being right will not stop another from suing you, and, being right can be very expensive in Intellectual Property litigation.
If she sues, one will “win” but that “win” will likely be as painful as any “loss”. Thus, if she sues, neither party is likely to “win” when all things are considered.
Why make a bunch of already rich lawyers richer?
I recommend you guys sign an agreement sharing ALL past works and “joint works” and start fresh from today forward.