Yeeaaahhh...So we're talking about a thin blade against a bigger block...If you don't think that sword and knife are analogous on this topic, I have nothing to say other than that you lack education in this department.
It is small to large comparison. The swords edge is small, while her arm is comparatively large. Not even 1% of the sword is relevant when talking about the cutting ability. Vast majority is entire for maintaining form and momentum. Only the first two or three first layers of ATOMS matter.
As for the ratio of material...Once again, you lack education in this department. As I said in my previous post, cutting ability depends on hardness AND size. It does NOT depend on material. What depends on material is hardness, and how small it can be made (for example, obsidian can be made into 1-atom wide edge, but steel needs more atoms to not fall apart).
It is completely irrelevant how many and what materials are in the blade nominally. Alloys are made to give new characteristics, but those new characteristics aren't additive. For all we know, the two metals are softer than her scales, so the resulting sword wouldn't ever be able to put a scratch on the actual scale since it would be softer. Likewise, either of the three materials could be difficult to work with, making the edge rather wide (for a functional blade), which would have a hard time cutting similarly hardened materials, even if thanks to its hardness it can cut through rocks like butter.
