I am not immediately familiar with her being in the Matter of France, but she was a character who was repeatedly exported into other peoples' folktales as far away as southern italy &, I think, Romania, so it would not surprise me
I can't remember how in depth it goes on Morgan's extracurriculars specifically, but Lucy Allen Patton's Studies In The Fairy Mythologies of Arthurian Romance is a FANTASTIC resource for a deep dive on how Morgan & other fey-themed characters fit in