This is the recommended mod, which will give Batgirl the haircolor from Harley (by using a hacked version of Harley's materials).

To install:
Unzip the pak and stick the pak in Mercury\Content\Paks\~mods

Overwrites Batgirl's hair texture without touching the materials. It sort of works (see screencaps), but is not quite as Blonde as using Harley's materials. To use it, REPLACE the other pak in ~mods. Only ONE of the paks should be installed.