X has been vivisected and dismembered multiple times in childhood. And adulthood. And young adulthood. She had her claws removed, coated in adamantium, and re-implanted in her body without anaesthetic when she was 7. She was irradiated in a chamber at that same age until she was almost dead so her healing factor would activate. She has a lot of cross-hatched scars on her forearms from her attempts to self-soothe etc while she was a weapon in a box. X doesn't talk about those, and she wears long gloves to hide them. They're her only actual physical scars.

Ysalwen has loads of scars, from fire, acid, lightning, blades, arrows, etc. Most of them aren't on her face.