Don't use Texture Filtering to fix frizzy hair textures. Instead, lower the Shading Rate. Lowering the shading rate to 0.5-0.2 will fix it, without screwing up the body textures. I often lower the shading rate on the hair anyway, just because it looks better.

It does take longer to render, so I only do it for the final render. (The Minimum Shading Rate in the Render Options menu overrides the setting for the individual items, so you can set that high for draft renders, then low for the final render, without having to change the setting for each object in the scene.)